It was examined whether sexual relationship characteristics were associated with condom use and safe sex practices against HIV. Characteristics investigated were: (1) age difference between sexual partners, (2) previous knowledge of partner, (3) type of relationship, (4) duration, and (5) exclusiveness. Safe sex practices (risky, non-safe, safe) were defined by condom use consistency, previous knowledge of partner and monogamy. Participants (N = 458, were Greek, sexually active and between 18-25 years old) responded to a questionnaire on sexual and condom use practices in their sexual relationships of the past 12 months, condom use negotiation and variables a-e. Only age difference between partners was found to differentiate consistent from inconsistent condom use. Inconsistent condom use was more frequent among partners whose age difference was over two years. Safe sex practices (risky, non-safe, safe) varied across different relationships of 36% and remained consistently non-safe or risky across those of 40%. Risky practices occurred more frequently in relationships where the man was older than the woman. When condoms had not been used, they had not been negotiated in 80% of the cases. These findings reconfirm the importance of negotiation in condom use, call attention to the neglected role of age differences between partners in safe sex and bring forward the issue of studying actual variation of safe sex practices across relationships as an indication of people's response to health campaign messages of risk reduction.