Use of health services is usually associated with a variety of factors, including the socioeconomic characteristics of the users, their familiarity with the usefulness of the services provided, and the acceptability and accessibility of those services. To study the factors associated with women's familiarity with the Pap test, a population-based study was carried out in Mexico City and two rural areas in the state of Oaxaca by means of household interviews. The sample consisted of 4208 women 15 to 49 years of age. Univariate, bivariate, and multivariate analyses were done using unconditional logistic regression; the independent variables were access to social security health services, age, education, housing quality, and place of residence (urban or rural); the dependent variable was the interview subject's familiarity with the purpose of the Pap test. The results were expressed as odds ratios with 95% confidence intervals. It was found that 41.5% of the women surveyed did not know the purpose of the Pap test, and that within this latter group, 97% had never had one. Factors found to be associated with not knowing the test's purpose were lack of access to the social security health services (OR = 1.9; 95% CI: 1.5-2.3); illiteracy (OR = 36.1; 95% CI: 17.9-72.7); and low socioeconomic level (OR = 2.9; 95% CI: 2.3-3.7). Also, rural dwellers had less familiarity with the Pap test than urban dwellers (OR = 0.5; 95% CI: 0.4-0.7). These results highlight the need to develop strategies for making the benefits of the Pap test known, bearing in mind the socioeconomic and cultural diversity of the populations involved.