This study describes the risk factors and the prevalence of HIV infection in a population of 744 prisoners, female prostitutes, homo-bisexual men and sailors in Cartagena, one of the most important tourist harbours on the Caribbean sea. Between November 1993 and April 1995 a cross sectional study was carried out on the prevalence and risk factors of HIV infection in a group of 434 men and 310 women who participated in voluntary testing and carne from i) two prisons, ii) the Public Clinic of sexually transmitted diseases (STD) iii) a bar frequented by homosexual men and iv) the harbour at Cartagena. lnformation was gathered using a standardized questionnaire. The overall prevalence of HIV infection was 2.14%. Homosexual men had the highest HIV prevalence with 12.3%, while prisoners had 2.5%, female prostitutes 0.7% and sailors 0.5%. The risk factors associated with HIV infection for al1 groups were being involved in homo-bisexual behaviour (prevalence ratio= 13 C195% 4.8-34.8) and anal sex (PR=7 C195%=2.4-19). Having sex with foreigners was associated in the bivariate analysis but it vanished in the multivariate analysis. These data confirm that the homosexual group is still the principal population at risk mainly through anal sex. It is interesting to note that HIV infection in prostitutes was lower than expected from studies in other Colombian cities. improvement in educational methods to reach people in lower socioeconomical strata is needed to decrease the trends in the HIV epidemic in Colombia among high risk groups such as men having sex with men.