Background: The reported HIV/AIDS cases in Egypt are still few. However, indigenous transmission of the virus has been reported and conditions for its further spread also exist in the country. A key element in developing a health education program for the primary prevention of HIV infection is the accurate assessment of HIV/AIDS related knowledge and practices of the targeted population. The purpose of the current study is to assess HIV/AIDS related knowledge and perceived threat and their determinants among patients attending Dermato-Venerology [DV] clinics and suspected to have sexually transmitted infections[STI]. Methodology: A representative sample of 700 patients suspected to have STIS were recruited, using the proportional allocation technique, from the seven public DV clinics in Alexandria. Patients were interviewed using a structured interview questionnaire. The questionnaire included data on socio-demographic characteristics, knowledge, perception of threat and practices related to HIV/AIDS. Stepwise multiple logistic regression analysis was performed to explore the effect of the different factors, with level of knowledge and level of perceived HIV/AIDS threat as dependent variablès. The independent factors were first individually correlated significantly with the dependent variables. Results: Majority of the patients were males; having up to nine years education with mean age 29.2 years ± 7.9. Less than 10% had good level of HIV/AIDS related knowledge. Misinformation on issues related to modes of HIV transmission was observed, where over half of the study population failed to identify breast feeding and tattooing as proved modes of transmission. On the other hand, 71.4%, 38.1% and 35.7% accused insect bite, sharing toilet and swimming places and household contact, respectively as modes of transmission. To prevent HIV infection, more than half of the sample mentioned avoiding practicing extramarital sex, while only 31.9% mentioned using condoms. Mass media mainly TV was the main source of information for the majority of patients. Regarding perceived susceptibility to HIV infection, only 29.1% of male patients had low perceived susceptibility compared to more than half the female patients. Participant's gender, educational level and age were the important predictors for knowledge level, while the first important determinant for perception of threat was patients' gender followed by patients' level of knowledge. Conclusion: It can be concluded that there was a significant number of persons among this risky group who did not know the basic facts concerning HIV/AIDS. There was great variation in the level of knowledge and perception of HIV/AIDS threat among this group. The r'? of health personnel as a source of information was very limited.