To assess smoking-related and other risk factors for high-grade cervical dysplasia in southwestern Hispanic and non-Hispanic white women in New Mexico, we conducted a clinic-based case-control study among attendees at university-affiliated gynecology clinics. We collected data on cigarette use, sexual behavior, past and current sexually transmitted diseases, hygienic practices, contraception, and diet. For both ethnic groups combined, after adjustment for the effects of human papillomavirus, sexual behavior, and other risk factors, cigarette smoking at the time of diagnosis was associated with high-grade dysplasia (odds ratio, 1.7; 95% confidence limits, 1.0-2.8). In contrast, former smoking was not associated with cervical dysplasia (odds ratio 0.9; 95% confidence limits, 0.5-1.5). Analyses showed dose-response relationships for the amount of cigarettes smoked per day and for cumulative exposure (pack-years of use) in association with cervical dysplasia. Although our study lacked the power to show statistically significant ethnic differences in smoking-related risks for dysplasia, smoking at the time of diagnosis, high pack-years of use, and smoking at the time of menarche were associated with dysplasia only for non-Hispanic white versus Hispanic women. Our data support hypotheses that implicate cigarette use as an etiological factor in the development of high-grade cervical dysplasia and suggest ethnic differences in risks for dysplasia among women attending the same clinics.