This study examines the prevalence of contraindications to the use of oral contraceptives in Mexico by sociodemographic characteristics and by whether this family planning method was obtained with or without a doctor's prescription. Using data on smoking behavior and blood-pressure measurements from the 2000 Mexican National Health Survey, the authors found that, under the 1996 World Health Organization (WHO) medical eligibility guidelines, the prevalence of contraindications is low and that no significant differences in contraindications exist at any level between those who obtain oral contraceptives at clinics and those who obtain them at pharmacies. In 2000, however, WHO substantially revised its criteria regarding the level of hypertension that would constitute a contraindication for oral contraceptive use. Applying the new guidelines, the authors found that 10 percent of pill users younger than 35 and 33 percent aged 35 and older have health conditions that are either relative or absolute (Category 3 or 4) contraindications. The relevance of these findings to the larger debate concerning screening and over-the-counter access to oral contraceptives is discussed.