Mutations in LRRK2 were recently identified in autosomal dominant Parkinson's disease (PD), including the G2019S mutation. To evaluate its frequency, we analyzed 198 probands with autosomal dominant PD, mostly from France and North Africa. Surprisingly, the frequency in North African families (7/17, 41%) was greater than those from Europe (5/174, 2.9%). The clinical features in 21 patients, including 1 with a homozygous mutation, were those of typical PD, with lower Mini-Mental State Examination scores. There were also 15 unaffected mutation carriers, aged 32 to 74 years. LRRK2 mutations appear to be a common cause of autosomal dominant PD, particularly in North Africa. Ann Neurol 2005;58:784–787