Sex workers play a major role in spreading sexually transmitted infections (STIs). We studied the prevalence rates and risk factors for STIs among 300 brothel-based sex workers in Tel-Aviv. Throat swabs were cultured for Neisseria gonorrhoeae, urine samples were tested by polymerase chain reaction (PCR) for Chlamydia trachomatis and N. gonorrhoeae, and sera were tested for syphilis, human immunodeficiency virus (HIV) and type 2 herpes simplex virus (HSV) antibodies. N. gonorrhoeae was cultured from throat samples of 9.0% of participants; PCR testing of urine was positive for C. trachomatis in 6.3% and for N. gonorrhoeae in 5.0%. Syphilis serology was positive (Venereal Disease Research Laboratory [VDRL] titres > 1:8) in 1.3% of women, HSV-2-specific immunoglobulin G was detected in 60% and HIV serology was positive in a single case (0.3%). Having STI was significantly associated with age, number of years in Israel, number of clients a week and condom use for vaginal sex. In a multivariate analysis, having STI was significantly associated with number of clients per week and condom use for vaginal sex. The high prevalence of pharyngeal gonorrhoea reflects most probably the expanding demand of clients for oral sex and the insufficient condom use in this form of sex.