The prevalence of cervical intraepithelial neoplasia (CIN) and the association of CIN with prostitution was examined in Oviedo, a region in Spain with low incidence of cervical cancer, and in Cali, Colombia, where the incidence of cervical cancer is 6-10 times higher. In Oviedo, the study included 758 prostitutes attending a sexually transmitted diseases clinic and 1203 nonprostitutes attending a family-planning clinic. In Cali, 775 prostitutes and 1795 nonprostitutes attending health centers were included. Seropositivity to common sexually transmitted agents was investigated in Spanish prostitutes. No significant difference was found in the prevalence of CIN between Oviedo and Cali in both prostitutes (2.5 versus 1.8%) and nonprostitutes (1.2 versus 1.1%). Prostitutes had a 2-fold increased risk of CIN as compared to nonprostitutes; in Spain, the prevalence odds ratio (POR) was 2.3 and the 95% confidence interval (CI) was 1.1-4.5, and, in Colombia, POR was 1.8 and the 95% CI was 0.9-3.5. Among prostitutes in Oviedo, human immunodeficiency virus (HIV) prevalence was 4.9% and HIV-positive prostitutes showed a high risk of CIN as compared to HIV-negative prostitutes (POR, 12.7; 95% CI, 3.9-40.9); 76% of HIV-positive prostitutes were i.v. drug users and showed an increased seroprevalence of other sexually transmitted diseases. HIV-negative prostitutes did not show any increased risk of CIN (POR, 1.2; 95% CI, 0.5-2.8). These results show that among nonprostitutes the prevalence of CIN was not statistically different between the two cities in Spain and Colombia; prostitutes were at moderate increased risk compared to nonprostitutes in both cities.(ABSTRACT TRUNCATED AT 250 WORDS)