Context: In most developing countries, the majority of sexually active female adolescents are married. Although married adolescents are often assumed to be at low risk for HIV infection, little is known about the actual HIV risks these adolescents face or about ways to minimize these risks. Methods: Demographic and Health Survey data from 29 countries in Africa and Latin America were used to examine the frequency of factors that may increase HIV risk in married women aged 15-19. Results: Several behavioral and social factors may increase the vulnerability of married female adolescents to HIV infection. First, these young women engage in frequent unprotected sex: In most countries, more than 80% of adolescents who had had unprotected sex during the previous week were married. Second, women who marry young tend to have much older husbands (mean age difference, 5-14 years) and, in polygamous societies, are frequently junior wives, factors that may increase the probability that their husbands are infected and weaken their bargaining power within the marriage. Third, married adolescents have relatively little access to educational and media sources of information about HIV. Finally, the most common AIDS prevention strategies (abstinence, condom use) are not realistic options for many married adolescents. Conclusion: New policies and interventions, tailored to the sexual and behavioral profiles of women in each country, are needed to address the vulnerabilities of adolescent wives. In some countries, delaying age at marriage may be an important strategy; in others, making intercourse within marriage safer may be more valuable.