Genital chlamydial infection has evolved as the leading sexually transmitted disease, both in the developed and the developing countries. The impact of genital chlamydial infection as a public health problem in the Caribbean is probably as high as in industrialized countries. Accurate statistics are therefore needed to obtain knowledge of the epidemiology of this disease. A prevalence study was carried out in Jamaica on persons attending different health facilities and locations. This was to ascertain the prevalence of chlamydial antibodies and of chlamydial infection in these selected populations. Microbiological methodologies employed were the microimmunofluorescent technique (MIF) for detecting antichlamydial antibodies, the direct immunofluorescent test (DFA) for detecting chlamydia antigens in specimens, and also isolation of C. trachomatis by culture in McCoy cells. A total of 1228 sera were tested for antichlamydial antibody resulting in the following seroprevalence rates. Prostitutes -95.3 percent, gynaecology patients -60.0 percent, family planning clinic attendess -59.8 percent, blood donors -52.6 percent, sexually transmitted diseases (STD) clinic patients -70.1 percent, pregnant women -25.0 percent. The 95.3 percent seroprevalence rate observed in prostitutes was significantly higher than that found in the other groups. From 1641 patients, specimens including urethral, endocervical, conjunctival and nasal swabs were cultured for C. trachomatis. The organism was isolated from 18.5 percent to 59.3 percent in this study group; in pregnant women 18.5 percent (n=200), neonates 24.0 percent (n=100), prostitues 24.8 percent (n=129), student 33.9 percent (n=103), family planning clinic attendess 34.0 percent (n=238), gynaecology patients 45.8 percent (n=170) and STD patients 59.3 percent (n=701). The seroprevalence of C. trachomatis is high in Jamaican population, although the rate of infection was found to be much lower. A wide cross-section of the Jamaican population in different age groups from different strata of the society and having different behavioural patterns was found to be infected with C. trachomatis. The prevalence of C. trachomatis infection was not influenced significantly by demographic factors or socioeconomic status, since both chlamydial antibody and C. trachomatis were demonstrated in all age groups and in individuals from different strata of the society with different behavioral patterns.