Parkinson's disease (PD) is the most common form of parkinsonism, affecting nearly 2% of people older than 65 years of age. Symptomatic treatment has been available for decades, but to date there is no treatment retarding disease progression. Over the past decade several genes causing parkinsonism have been identified in families with a mendelian pattern of inheritance. The most recent is the leucine-rich repeat kinase 2 (LRRK2) gene. Pathogenic mutations in the LRRK2 gene cause a significant proportion of clinically typical, late-onset PD. This review summarizes the current knowledge on the contribution of LRRK2 mutations in understanding parkinsonism.