OBJECTIVE: To describe the epidemiology of HIV infection in the Manya Krobo District, Ghana, and its potential link to the building of the Akosombo dam. METHODS: A questionnaire and a blood sample were collected among 1228 consecutive pregnant women seen at the prenatal clinics of the two major hospitals of the district. RESULTS: Overall, prevalence of HIV and of serologically confirmed syphilis were 14.9% and 0.7%, respectively. HIV infection was more prevalent among the Krobo ethnic group (137 of 742 [18.5%]) than among other ethnic groups (46 of 486 [9.5%]; p <.001). Two distinct patterns of HIV distribution were identified. Among the Krobos, HIV was common among all age groups, reached a plateau (21.9%) in the 30- to 34-year-old group and was associated strongly with having lived in Côte d'Ivoire and with having received only primary school education. Among the other ethnic groups, prevalence decreased with age, from 17.2% in the 13- to 19-year-old age group to 1.4% among women aged 35 years or older, and HIV infection was associated with having had first sexual intercourse before the age of 17 years. In logistic regression analysis, the independent risk factors for HIV infection were age, schooling, age at first sexual intercourse; having lived in Côte d'Ivoire; age and schooling showed significant interactions with ethnic group. CONCLUSIONS: The high HIV prevalence documented in this part of Ghana seems to be, to some extent, a consequence of construction of the Akosombo dam in the 1960s. The flooding of the land, the failures of the resettlement program and the ensuing poverty prompted economically driven migration, specially to Côte d'Ivoire, where many migrants became infected with HIV. Local transmission followed. This illustrates that HIV can disseminate widely in a society where most men are circumcised and where genital ulcerative diseases are uncommon and should be an indication for less complacency about HIV control in West Africa.