In this study involving 1286 LRRK2 G2019S carriers corresponding to 1621 person-years of follow-up (1292 person-years at risk of PD) and 109 154 non-carriers, we show that the predicted cumulative incidence of PD in LRRK2 G2019S carriers by age 60 is 9% and 49% by age 80 years. This evidence concerns the gene LRRK2 and Parkinson disease.