This study in 2003 looked at knowledge, attitudes and behaviours concerning HIV among 3 high-risk groups (201 cross-border truck drivers, 50 female sex workers and 754 youths) in 4 cities in the Islamic Republic of Iran. The level of knowledge about HIV was low on average, especially among individuals with high-risk behaviours. Truck drivers and female sex workers had higher knowledge about sexually transmitted infections than youths but their knowledge came primarily from personal experience rather than public awareness programmes. Truck drivers had a more positive attitude to temporary marriage and pre- and extramarital sex than youths. Condom use was low in all groups. Better targeted education of high-risk groups is needed.