To assess knowledge and attitudes about HIV/AIDS in Mashhad, 960 people aged 13-58 years who were approached in the street and agreed to participate completed an anonymous questionnaire. The mean of knowledge and attitudes scores were 9.8 (SD 3.0) and 6.1 (SD 3.0) of a total 14 and 10 respectively. People with greater knowledge of HIV/AIDS had more positive attitudes to individuals with HIV/AIDS (P < 0.01). There were important misconceptions about HIV transmission such as through hugging, food, clothing, public places and insect bites. Regression analysis indicted that women had more tolerant attitudes than men (P < 0.01) and the more educated respondents had higher knowledge and attitudes scores (P < 0.0001 and P < 0.001 respectively).