Public health authorities have long believed that the preponderance of AIDS cases in Africa are attributable to `heterosexual transmission’; most people silently assume this rubric to indicate penile± vaginal intercourse only. Recent epidemiologic analyses suggest that the majority of HIV cases in sub-Saharan Africa may be due to non-sterile health care practices. The present paper reviews the anthropological, proctologic, and infectious disease literature, and argues that both homosexuality and heterosexual anal intercourse are more prevalent in Africa than has traditionally been believed. The authors hypothesize that perhaps the majority of HIV transmission not accounted for by iatrogenic exposure could be accounted for by unsuspected and unreported penile± anal intercourse. Given the authors’ findings, properly conducted studies to measure this HIV transmission vector, while controlling for iatrogenic exposure confound, are clearly warranted in Africa and in countries with similar epidemiologic characteristics.