The authors determined the GSTM1 genotype of 190 Caucasian women with invasive squamous cell cervical cancer in western Washington State between January 1986 and June 1994 and of 206 controls. It was found that 53% of cases and 57% of controls had the GSTM1 null genotype. The age-adjusted odds ratio associated with GSTM1 null genotype was 0.8 (95% confidence interval 0.6, 1.3). The lack of association between cervical cancer risk and GSTM1 genotype was true both for smokers and nonsmokers of cigarettes and for heavy and light smokers. These data suggest that women with the GSTM1 null genotype are not at increased risk of cervical cancer.