Context: An entertainment-education radio soap opera, Apwe Plezi, was broadcast from February 1996 to September 1998 in St. Lucia. The program promoted family planning, HIV prevention and other social development themes. Methods: The program's effects were assessed through analyses of data from nationally representative pretest and posttest surveys, focus-group discussions and other qualitative and quantitative sources. Results: Among 1,238 respondents to the posttest survey, 35% had listened to Apwe Plezi, including 12% who listened at least once per week. Multivariate analyses show significant effects of both time and listenership category on several knowledge, attitude and behavior variables. For example, 16% of posttest respondents knew a slang term for condoms that was coined for the radio program, and the proportions of respondents who considered it acceptable for husbands to have sex partners outside their marriage declined from 27% in the pretest to 14% in the posttest survey. Compared with nonlisteners, regular listeners were more likely to trust family planning workers (83% vs. 72%) and considered a significantly lower number of children the ideal (2.5 vs. 2.9). Fourteen percent of listeners reported having adopted a family planning method as a result of listening to the program. Conclusion: Apwe Plezi influenced listeners to increase their awareness of contraceptives, improve important attitudes about fidelity and family relations, and adopt family planning methods. Important lessons for entertainment-education programmers include that program reach, and therefore effects, can be limited by competition with other programming, and that monitoring listeners' perceptions is essential to detect and correct misinterpretations of program messages.