The purpose of this study was to examine the relationship of perceived risk, outcome expectancies, and perceived self-efficacy to intention and in turn exercise behavior. A convenience sample of people 18 years or older (N = 645) was recruited from public locations in Thailand. A descriptive cross-sectional design was used with self-administered questionnaires. Path models were estimated using Amos 18. Outcome expectancies and perceived self-efficacy indirectly influenced exercise behavior via intention. Unexpectedly, perceived risk of heart disease did not contribute to the model. Differences were found across age and gender groups. The final models showed a better fit in the middle-aged group, Χ2(1) = 0.374, p = .541, and in women, Χ2(1) = 0.197, p = .657, than in younger individuals and men. Interventions that enhance intention to exercise through outcome expectancies and perceived self-efficacy may be effective. Interventions may be more effective if they target particular age and gender groups.