In Vienna, legalized prostitution is tightly controlled by the advisory board of the Viennese Public Health Service. Registered prostitutes are routinely screened for all important STDs, such as syphilis, HIV, gonorrhea, chlamydial- and yeast-infections, and Trichomonas vaginalis. Furthermore, cytological smears are obtained from the cervix and chest X-rays are performed at least once a year. In all pathological findings, an appropriate therapy is implemented. Presenting data of 1989, out of the 713 weekly controlled registered prostitutes, Neisseria gonorrhoeae was detected in 0.3% of all examinations (110/35,368). In non-registered prostitutes, the infection rate of N. gonorrhoeae was 6.9% (27/354), and so far, 20 times higher than in registered ones. The infection rate of Chlamydia trachomatis, which has been routinely diagnosed in registered prostitutes for several years, has decreased from 20.4% in 1980 to 2.2% in 1989 compared with 31.4% and 10.9% in non-registered prostitutes. In registered prostitutes, the prevalence of genital infections, such as C. trachomatis, T. vaginalis, and yeasts was shown to be 4.9%. The corresponding data in non-registered prostitutes were much higher (18.8%). Due to examinations for cervical malignancy the incidence of Papanicolaou stain IV and V has decreased from 3.1% in 1988 to 1.6% in 1989. There was no serologic evidence for syphilis and HIV infection in both special risk groups. The data demonstrate, that due to a good health surveillance of STD-risk groups, a good information service, and free treatment, the prevalence of STDs can be reduced in prostitutes.