Parkin gene mutations are reported to be a major cause of early-onset parkinsonism (age at onset < or = 45 years) in families with autosomal recessive inheritance and in isolated juvenile-onset parkinsonism (age at onset <20 years). However, the precise frequency of parkin mutations in isolated cases is not known. In order to evaluate the frequency of parkin mutations in patients with isolated early-onset parkinsonism according to their age at onset, we studied 146 patients of various geographical origin with an age at onset < or = 45 years. All were screened for mutations in the parkin gene using semi-quantitative polymerase chain reaction combined with sequencing of the entire coding region. We identified parkin mutations in 20 patients including three new exon rearrangements and two new missense mutations. These results, taken in conjunction with those of our previous study (Lücking et al., 2000) show that parkin mutations account for at least 15% (38 out of 246) of our early-onset cases without family history, but that the proportion decreases significantly with increasing age at onset. There were no clinical group differences between parkin cases and other patients with early-onset parkinsonism. However, a single case presenting with cerebellar ataxia several years before typical parkinsonism extends the spectrum of parkin related-disease.