A cross-sectional survey was conducted among 124 street- and brothel-based female commercial sex workers (CSWs) in Georgetown in January and February 1997 to determine the seroprevalence of human immunodeficiency virus (HIV) infection and describe the sexual practices and drug use patterns. Their median age was 30 years (range 17 to 52 years). 119 (88%) reported regular alcohol consumption while looking for clients, 27 (22%) said they smoked cocaine and 51 (42%) reported use of marijuana. Street-based CSWs were significantly more likely to report marijuana use (p = 0.033). 72% reported that they never used condoms with regular sex partners and 35% reported that they never used condoms with clients. Brothel-based women were significantly more likely to report consistent condom use with their clients (p = 0.05). 46% (54/118) tested HIV positive and 28% (33/118) had a positive serological test for syphilis. Factors that were significantly associated with HIV infection included a positive serological test for syphilis (OR = 7.56; 95% CI = 2.7-21.97; p < 0.01) and a history of having received treatment for syphilis (OR = 2.93; 95% CI = 1.12-7.8). Weak associations were also found between HIV infection and a history of cocaine use (OR = 2.57; 95% CI = 0.95-7.11; p = 0.039); having more than four clients per night (OR = 5.14; 95% CI = 1.65-16.74; p = 0.04); and a history of receiving treatment for salpingitis (OR = 2.31; 95% CI = .93-5.75; p = 0.0035). No statistically significant association was found between HIV infection and marijuana use nor any sociodemographic variables (age, place of work, and duration of sex work). There is an urgent need for a community based behavioural intervention programme targetting this high risk population.