This study investigated knowledge, beliefs, and practices related to STDs and AIDS among clients of low price sex workers in Bali, Indonesia. These men are at high risk of STD and HIV transmission. They have poor knowledge of the basic concepts of STD and HIV transmission and prevention, and they practice a variety of ineffective prevention strategies including partner selection and the prophylactic use of antibiotics. They report a mean of 1.9 paid sexual partners in the previous week and very low frequencies of condom use. Over 25% had experienced an STD symptom in the previous 6 months, with self treatment with antibiotics reported by a third. Recent experience of an STD was related to the number of sex worker partners in the previous month and to ever having used a condom with a sex worker. The implications of the study findings for the development of comprehensive STD control programs including educational campaigns, condom promotion, and the strengthening of STD case management by health care providers are discussed