Matrix metalloproteinases (MMPs), a family of closely related enzymes that degrade the extracellular matrix, are likely to be involved in invasion and metastasis of tumor cells. A guanine (G) insertion/deletion polymorphism within the promoter region of MMP-1 influences the transcription of this gene; i.e., the 2G (insertion-type) promoter possesses greater transcriptional activity than the 1G (deletion-type) promoter. To investigate whether this feature contributes to cancer development and/or progression, we genotyped 163 ovarian cancer patients for the polymorphism and then analyzed levels of expression of the MMP-1 gene in their tumors. The proportion of patients who were either heterozygotes or homozygotes for the 2G allele was significantly higher than that observed among 150 individuals without cancer (P = 0.028). Moreover, the levels of MMP-1 expression in cancer tissues among the patients carrying 2G alleles were elevated significantly in comparison with 1G homozygotes (P = 0.0038). By stimulating degradation of extracellular matrix, an excess of MMP-1 production may enhance development and/or rapid progression of ovarian cancers.