Objective: The Lrrk2 kinase domain G2019S substitution is the most common genetic basis of familial and sporadic parkinsonism. Patients harboring the G2019S substitution usually present with clinical Parkinson's disease. Methods: Herein, we report that the most common neuropathology of G2019S-associated Parkinson's disease is Lewy body disease. Results: Lrrk2 G2019S was observed in approximately 2% (n = 8) of our Parkinson's disease/Lewy body disease cases (n = 405). The mutation was also found in one control subject and one Alzheimer's disease patient, reflecting reduced penetrance. Interpretation: Therapeutic strategies targeted at modulating Lrrk2 kinase activity may be important to treat patients with genetically defined familial or typical sporadic Parkinson's disease.