A community based sample survey of sexually transmitted diseases and Human Immuno deficiency Virus infection was carried out among commercial sex workers of a red-light area in Calcutta. In this paper socio-demographic aspects of sex workers are discussed. For the survey, 450 sex workers were selected by random sampling method. Among the sex workers surveyed, 84.89 per cent were in the age group 15-29 years. Lowest age was 13 years and mean age was 23.12 years. Large number of sex workers were from Nepal (15.11 per cent) and Bangladesh (11.78 per cent). About 38 per cent were from three districts of West Bengal bordering Bangladesh. About 84.44 per cent of the sex workers were illiterate. Extreme poverty forced 49.10 per cent to choose this profession and family disturbances led 21.56 per cent to this profession. Almost all sex workers (448) had addiction, alcohol being taken regularly by 81.11 per cent. Number of clients of sex workers varied from 2 to 10, average being 3. About 67.33 per cent gave history of pregnancy, 46 per cent had abortion and 41.11 per cent had living children. About 27.11 per cent took precaution against pregnancy regularly. Use of oral pills was found to be the most common practice against pregnancy (13.65 per cent), followed by ligation (11.56 per cent). Only 1.11 per cent reported that their clients used condom regularly.