We analysed chromosome 3p for loss of heterozygosity (LOH) in 48 primary oral squamous cell carcinomas (SCCs) using 15 markers and constructed a deletion map for this chromosome arm. LOH at one or more loci was found in 34/48 (71%) of tumours. The data support the existence of at least three distinct regions of deletion at 3p24-26, 3p21.3-22.1 and 3p12.1-14.2. A significant correlation was observed between the number of regions showing allele loss at 3p and tumour stage, consistent with the progressive accumulation of genetic errors during the development of oral SCC. There were also significant associations between LOH at 3p and disease-free and overall survival of patients with early stage disease. This study is the first to demonstrate the prognostic significance of LOH at 3p for oral cancer and may help to identify patients who should receive more aggressive treatment.