Genetic alterations are believed to be important in the origin and dissemination of breast cancer. Cytogenetic rearrangements on chromosome 7 are common in breast tumours. We used the c-met proto-oncogene probe, which detects sequences on chromosome 7q31, to analyse tumour and blood leucocyte DNA samples from 245 patients with primary breast cancers. The pmetH polymorphic probe detected a high frequency of allele loss (40.5%) among the 121 informative (heterozygous) patients. This genetic alteration was not significantly associated with standard prognostic features including tumour size, histopathological grade, and lymph-node or steroid receptor status. However, patients with loss of heterozygosity on chromosome 7q31 in primary tumour DNA had significantly shorter metastasis-free survival (p = 0.00022) and overall survival (p = 0.0036) after surgery than patients without this alteration. These findings indicate that this region of chromosome 7 might be the site of a breast tumour or metastasis suppressor gene.