Aims: To investigate UK university student drinking in terms of social and motivational factors. Design: Quantitative and qualitative studies. Participants: Undergraduate students at a UK university: 50 "heavy drinkers" and 49 "light drinkers", equally distributed in terms of sex and year of study. Data: Questionnaire measures of drinking expectancies, perceived benefits and drawbacks of drinking, important people and activities; semi-structured interviews. Findings: Heavy drinkers scored higher than light drinkers on measures of tension reduction, sexual enhancement and dependency drinking expectancies. The top three reported benefits of drinking were social life, fun/humour, and self-confidence. Heavy drinkers perceived "a lot" of drawbacks to their finances as a result of drinking, whereas for light drinkers the main drawbacks concerned physical wellbeing. Heavy drinkers were found to interact with a heavier drinking social network, receive more encouragement to drink from important people in their lives and to participate in more heavy drinking activities than light drinkers. A tentative model was developed from the qualitative study suggesting that social factors are important influences in the maintenance of heavy student drinking, in particular subtle forms of "peer pressure", and increased self-confidence. Conclusions: Motivational factors, particularly the expectation of increased self-confidence, play an important role in the maintenance of heavy student drinking, but social factors are probably equally significant. The levels and patterns of heavy drinking found in the present sample are worrying and the findings have implications for attempts to reduce alcohol consumption by university students.