The extent of infection among 722 residents of an endemic focus of zoonotic Crimean-Congo hemorrhagic fever (CCHF) virus in rural northern Senegal, and putative modes of transmission were studied by a cross-sectional seroprevalence survey performed from February through May, 1989. Anti-CCHF virus IgG was found in13,3% of 283 persons who completed a standardized questionnaire and provided blood samples. Seropositivity rates were similar between sexes and increased significantly with age among nomadic persons. Risks appeared to be multifactorial. Behavior patterns, providing exposure to these risks were gender-based. Male risk were primarily associated with herding activities, and included sleeping outside during seasonal migrations, bite by tick (adult male Hyalomma truncatum), tick bite during the cool dry season, and sick animal contact. Sleeping outside was also a risk factor for nomadic women. Human infection has occurred more frequently or with less mortality regionally than elsewhere in Africa; Hyalomma ticks appear to be the primary transmission mode.