The prevalence and family structure of idiopathic Parkinson disease (iPD) in Turkey is not known. Patients with iPD were recruited consecutively at the Medical School of Istanbul University over an 18-month period. Clinical details were assessed with standardized forms. Of the 219 iPD patients, 136 had sporadic iPD [26 with parental consanguinity (cs)], 20 autosomal recessive PD (9 with cs) and 63 autosomal dominant or pseudo-dominant inheritances (20 with cs). Age at onset was 49.1 +/- 17.1 years (range 3-83) and age at examination 56.4 +/- 16.5 years (range 4-93). Ages at examination and at clinical onset of PD were significantly greater in sporadic iPD than in familial iPD patients, but disease duration was similar. Patients with familial PD had significantly lower basal UPDRS III and Hoehn and Yahr scores than sporadic PD patients and brisk reflexes in the lower limbs were significantly more frequent, but they suffered less from mictional problems. The frequency of familial PD and consanguinity in Turkey is higher and age at onset of iPD earlier than in Western countries. Molecular diagnoses and genetic counseling will therefore have a very important impact on the medical, psychological, and familial handling of PD in Turkey.