This paper describes perceptions of the societal acceptability and acceptability among peers of different types of premarital heterosexual relationships in Iran. Sources of variation in subjective norms are assessed. Results derive from a survey conducted in 2005 of a representative sample of 1743 female college students from four multidisciplinary universities in Tehran using two-stage random cluster sampling. An anonymous pilot-tested questionnaire was used. Respondents displayed remarkable heterogeneity and ambiguity concerning the social acceptability of premarital heterosexual friendship, dating and physical contact, but expressed greater certainty about the unacceptability of premarital sex. The majority (77.5%) reported that premarital sex was socially prohibited, while about one third (33.1%) were unsure about the social acceptability of having a boyfriend and dating before marriage. Peer norms were perceived to be more liberal but, nevertheless, very few peers were thought to be in favour of premarital intercourse. Older students, those with educated fathers and those studying in a mixed-sex university perceived norms to be more liberal than their counterparts. Access to satellite television, a major source of exposure to new information and values about sexuality, was a major predictor of liberal peer norms. It appears that a significant proportion of young people in Tehran have broken with tradition with regard to premarital social interaction and romantic friendships, but the majority still conforms to traditional cultural and religious values regarding abstinence before marriage.