- Unlabelled: Until now, research on sexual behavior and HIV in Israel has been carried out mainly on the general population, and focused primarily on defining populations at risk, without adequate consideration given to the reasons bringing these populations to be tested, and their specific sexual behaviors. In Israel, one can choose whether to take an HIV test in confidential centers (giving one's name under medical confidentiality) or in anonymous centers (Israel AIDS Task Force in Tel Aviv and Beer Sheva, Levinsky Clinic in Tel Aviv and Haparsim Clinic in Haifa]. At least 21% of the clients of the anonymous testing centers in Israel belong to a high risk population in contrast to 2.6% in confidential clinics, and so, in this study, we hypothesize that characterization of sexual behavior patterns in anonymous testing centers might enable us to better characterize sexual behavior patterns in high risk populations. Methods: In this cross-sectional study, we used questionnaires distributed in the clinics by the Israel AIDS Task Force in order to characterize their clinic's clients. The questionnaires were completed by the Israel AIDS Task Force consultants during the consultation period at which the anonymous test was performed. Data collected included: gender, age, testing history, specific sexual behaviors and reasons for applying for the current test. Results: A total of 926 questionnaires were collected; 29.9% of them were of female patients. The average age was 29.47 years (1±8.66]; 21.3% of the clients were men who have sex with men [MSM]; only 2.3% of the clients belonged to other high risk populations. In all groups, the majority of the patients reported high risk sexual behavior (any sexual contact without a condom) and the average age for the first test was much higher than the average age of first sexual intercourse common in Israel. Women reported more participation in unprotected vaginal intercourse than heterosexual men, and a substantial part of MSM reported performing unprotected anal intercourse. More heterosexuals than MSM stated a new relationship as a reason for applying for the test, and more MSM than heterosexuals reported arriving for a routine check-up. Conclusions: There is a need for comprehensive programs encouraging testing for HIV in all age groups, focusing on Sthe ages 18-25 years, and encouraging the use of a condom as a preventive measure in all populations, especially women. We feel it is essential to emphasize the need for educational programs tailored for each sub-population's psychosocial characteristics and specific issues.