The purpose of the study was to determine the applicability of the Transtheoretical Model for predicting unprotected intercourse in HIV+ Thai youth. Questionnaires and interviews about sexual behaviour, readiness to change, self-efficacy, substance use, emotional distress and social support were obtained from 70 HIV+ Thai youth (ages 17 to 25). Path analysis suggested the model was an excellent fit with the data. Readiness to change but not self-efficacy was directly related to unprotected intercourse acts. This differed from HIV+ youth in the US where self-efficacy fully mediated the relationship between readiness to change and condom use. In the Thai sample, social support and self-efficacy were indirectly related to unprotected intercourse through stage of change. Substance use was unrelated to unprotected intercourse, but rates of use were low. Potential cultural differences in the construct of self-efficacy and its relationship to risky behaviours in Thailand require further study. However, results highlight the potential of prevention interventions that increase readiness to change through boosting self-efficacy and social support specific to practicing safer sex while addressing mental health concerns.