We performed a clinical genetic analysis of a kindred originating in the town of Contursi in Salerno province, Italy, in which 60 individuals in 5 generations are known to have had Parkinson's disease (PD). Two previously reported autopsy cases showed typical PD with Lewy bodies. The inheritance pattern is apparenly autosomally dominant with a segregation ratio of 40.1% for kindred members aged 50 years and older. The mean age at PD onset is 45.6 years (standard deviation, 13.48; range, 20–85) with a mean course to death of 9.2 years (standard deviation, 4.87; range, 2–20). Otherwise, clinical characteristics of PD in the kindred, including variance in onset age and incidence of tremor and levodopa responsiveness, are similar to those of PD in the community. The presence of tremor tended to be concordant in affected parent-child pairs, but there was no parent-child correlation for age at onset or intrasibship clustering of tremor or onset age. A suggestin of anticipation disappeared after adjustment for age-relted ascertainment bias. The findings show that a presumably single mutation can prodcue a heterogeneous PD phenotype, even among siblings. This is consistent with the hypothesis that PD in the community may in fact be caused by sch a mutation, but one producing a lower penetrance and older age at onset than those in this kindred.