Communicating about sex is a vital component of human immunodeficiency virus (HIV) prevention and influences how HIV educators convey messages to communities and how couples negotiate safer sex practices. However, sexual communication inevitably confronts culturally based behavioral guidelines and linguistic taboos unique to diverse social contexts. The HIV interventionist needs to identify the appropriate language for sexual communication given the participants and the message. Ethnographic research can help facilitate the exploration of how sex terminology is chosen. A theoretical framework, developed to guide HIV interventionists, suggests that an individual's language choice for sexual communication is influenced by gender roles and power differentials. In-depth interviews, free listing and triadic comparisons were conducted with Xhosa men and women in Cape Town, South Africa, to determine the terms for male genitalia, female genitalia and sexual intercourse that are most appropriate for sexual communication. Results showed that sexual terms express cultural norms and role expectations where men should be powerful and resilient and women should be passive and virginal. For HIV prevention education, non-mother tongue (English and Zulu) terms were recommended as most appropriate because they are descriptive, but allow the speaker to communicate outside the restrictive limits of their mother tongue by reducing emotive cultural connotations.