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INTRODUCTION: Many authors have described these last years the difficulty to establish a differential diagnosis between schizophrenia and frontotemporal dementia. However treatment and prognosis of these two separate diseases are not the same. Schizophrenia is a chronic syndrome with an early onset during teenage or young adulthood period and the major features consist of delirious ideas, hallucinations and psychic dissociation. However a large variety of different symptoms describes the disease and creates a heterogeneous entity. The diagnosis, exclusively defined by clinical signs, is then difficult and has led to the research of specific symptoms. These involve multiple psychological processes, such as perception (hallucinations), reality testing (delusions), thought processes (loose associations), feeling (flatness, inappropriate affect), behaviour (catatonia, disorganization), attention, concentration, motivation (avolition), and judgement. The characteristic symptoms of schizophrenia have often been conceptualised as falling into three broad categories including positive (hallucination, delision), negative (affective flattening, alogia, avolition) and disorganised (poor attention, disorganised speech and behaviour) symptoms. No single symptom is pathogonomonic of schizophrenia. These psychological and behavioural characteristics are associated with a variety of impairments in occupational or social functioning. Cognition impairments are also associated with schizophrenia. Since the original clinical description by Kraepelin and Bleuler, abnormalities in attentional, associative and volitional cognitive processes have been considered central features of schizophrenia. Long term memory deficits, attentional and executive dysfunctions are described in the neurocognitive profile of schizophrenic patients, with a large degree of severity. The pathophysiology of schizophrenia is not well known but may be better understood by neuronal dysfunctions rather than by a specific anatomical abnormality. Frontotemporal lobar degeneration (FTLD) is one of the most common causes of cortical dementia. FTLD is associated with an anatomical atrophy that can be generalised, with a frontotemporal or focal lobar predominance. Histologically there is severe neuronal loss, gliosis and a state of spongiosis. In a minority of case Pick cells and Pick bodies are also found. The usual clinical features of FTLD are divided in three prototypic syndromes: frontotemporal dementia (FTD), progressive non-fluent aphasia (PA) and semantic dementia (SD). FTD is the most common clinical manifestation of FTLD. FTD is first characterised by profound alteration in personality and social conduct, characterised by inertia and loss of volition or social disinhibition and distractibility. There is emotional blunting and loss of insight. Speech output is typically economical, leading ultimately to mutism, although a press of speech may be present in some overactive, disinhibited patients. Memory is relatively preserved in the early stage of the disease. Cognitive deficits occur in the domains of attention, planning and problems solving, whereas primary tools of language, perception and spatial functions are well preserved. PA is an initial disorder of expressive language, characterised by effortful speech production, phonologic and grammatical errors. Difficulties in reading and writing also occur but understanding of word meaning is relatively well preserved. In SD a severe naming and word comprehension impairment occur on the beginning in the context of fluent, effortless, and grammatical speech output. There is also an inability to recognise the meaning of visual percepts. The clinical syndromes of FTLD are associated with the brain topography of the degeneration. So considerable clinical overlap can exist between schizophrenia and FTLD and the object of the following case report is to remind the difficulty to make a differential diagnosis between these two pathologies. CASE REPORT: A 34 year old non-married man is admitted in mental health district of a general hospital for behavioural disturbances that include repeated aggressions towards his family. At initial interview visual and auditives hallucinations are described. The patient doesn't care about these abnormalities and a poverty of speech is observed. The affects, globally blunted, show some degree of sadness however. The patient's birth and early development were unremarkable. At the age of 26, the patient dismissed from his job because of poor performance and absenteeism. He spent a lot of time watching TV, showed poverty of speech and become sometimes angry and violent without an explanation. He was hospitalised for several months and a schizophrenia including predominant negative features, hallucinations and delusion was diagnosed. He was treated with bromperidol, could go back to home and was followed by a general practitioner for 8 years. The patient had a stereotyped way of life during these years with a poor communication and little activity. During the months preceding the current hospitalisation, these characteristics and avolition emphasised, urinary incontinence appeared. The patient receives risperidone 8 mg/day associated with citalopram 40 mg/day during several months of hospitalisation. No significant evolution is observed regarding apathic and stereotyped way of live. The capacity of communication remains very poor. Neurocognitive assessments reveal multiple and severe dysfunctions. Memory, executive and attentional tasks are extremely disturbed. Physical and neurological examinations reveal an isolated bilateral Babinski sign. Cerebral scanner and magnetic resonance show bifrontal atrophy and PET scan is normal. There are no significant abnormalities found on blood and urine samples and on lumbar puncture. The patient is sent to a chronic neuropsychiatric hospital and the treatment is stopped. One year later, a comparative evaluation is realised. The general clinical state shows no evolution. Neurocognitive assessments are repeated and severe dysfunctions are observed with more perseverations. DISCUSSION: A diagnosis of FTLD for this patient can be discussed regarding clinical features, neurocognitive testings and neuroradiological findings. Schizophrenia is a major differential diagnosis. Psychotic symptoms like hallucinations and age of onset are essential observations for the diagnosis of schizophrenia but can not exclude FTLD. Memory, intellectual functions, executive and attentional abilities may all be disturbed in schizophrenia and FTLD. Cerebral abnormalities well established in schizophrenia are lateral ventricles enlargements. Frontal lobar atrophy is a major argument for FTLD and is only a sporadic finding in schizophrenic populations. Schizophrenia and FTLD could be comorbid diseases by several ways. CONCLUSION: A differential diagnosis between schizophrenia and FTLD is difficult to establish. Schizophrenia is a heterogeneous disease with a large variety of cognitive dysfunctions. Neurocognitive tools may improve our knowledge of schizophrenia.