We report the clinical, genetic, and neuropathological findings of a seven generation-spanning pedigree with 196 individuals, 25 of whom had levodopa-responsive parkinsonism. Genetic analyses indicated Parkin mutations in 77 subjects. Among the 25 patients, 5 carried compound heterozygous mutations and met criteria for definite Parkinson's disease (PD) according to UK PD Society Brain Bank guidelines; 8 subjects carried only a heterozygous Parkin mutation. The mutational status of five deceased patients was unknown, and seven PD patients had no Parkin mutation. Survival analyses showed a significant difference in the age-at-onset distribution between patients with compound heterozygous mutations and the groups of heterozygous carriers and subjects without detectable Parkin mutations. Autopsy of a 73-year-old patient, who carried two mutant Parkin alleles (delExon7 ؉ del1072T), showed PD-type cell loss, reactive gliosis, and ␣-synuclein-positive Lewy bodies in the substantia nigra and locus ceruleus. Surviving neurons were reactive with antibodies to the N terminus of Parkin but not the In-Between-RING ("IBR") domain, which had been deleted by both mutations. This large Parkin pedigree represents a unique opportunity to prospectively study the role of heterozygous Parkin mutations as a PD risk factor, to identify additional contributors to the expression of late-onset PD in heterozygous carriers, and to reexamine the role of Parkin in inclusion formation.