OBJECTIVE To investigate the cognitive profile of first degree relatives of patients with familial Parkinson's disease to determine whether these subjects presented signs of neuropsychological dysfunction compared with healthy controls. Results of recent genetic and neuroimaging studies suggest a genetic contribution to the aetiology of Parkinson's disease and underline the interest in identifying preclinical signs of the disease. METHODS A battery of tests evaluating executive function was administered to 41 first degree relatives of patients with well documented familial Parkinson's disease and 39 healthy controls. A factorial discriminant analysis allowed isolation of a subgroup of 15 first degree relatives who could be considered as impaired compared with the healthy controls. Among these 15 "deviant" relatives, nine performed globally worse than the control subjects on all tasks. The six other subjects had mean or even high scores on all task variables, except on those highly correlated with the discriminant score of the factorial discriminant analysis. CONCLUSIONS Among the first degree relatives of patients with familial Parkinson's disease, some manifested executive dysfunction comparable with that typically associated with the disease. Such impairment could represent a preclinical form of Parkinson's disease.