Familial Parkinson's disease (PD) has been linked to missense and genomic multiplication mutations of the α‐synuclein gene (SNCA). Genetic variability within SNCA has been implicated in idiopathic PD in many populations. We now confirm and extend these findings, within a Belgian sample, using a high‐resolution map of genetic markers across the SNCA locus. Our study implicates the SNCA promoter in susceptibility to PD, and more specifically defines a minimum promoter haplotype, spanning approximately 15.3kb of sequence, which is overrepresented in patients. Our findings represent a biomarker for PD and may have implications for patient diagnosis, longitudinal evaluation, and treatment. Ann Neurol 2004;56:591–595