The applicability of the Theories of Reasoned Action and Planned Behaviour to the cooperative behaviour of condom use were examined. Seventy-one male and 78 female students, all sexually active unmarried heterosexuals aged 17 to 21 years, gave information about their intentions for the next sexual encounter, as well as their attitude, subjective norm, expectancy-value attitude and subjective norm (including normative beliefs for their sexual partner), and their past behaviour with respect to condom use. After their next sexual encounter, they completed a questionnaire on their actual condom use. Results indicated that when behavioural conditions including the availability of a condom and an agreement with the partner to use it were satisfied, intention interacted with past behaviour to predict actual behaviour. These results imply that intentions which are consistent with past behaviour are stable enough to be carried out in the face of the interpersonal dynamics of a sexual encounter. Further, normative belief for the sexual partner had a direct influence on attitudes, subjective norm and intention. Neither the Theory of Reasoned Action nor the Theory of Planned Behaviour can fully explain these results, which point to the need for further theoretical inquiry into the dynamics of cooperative behaviour.