Drawing from self-determination theory (SDT), this study examined the effect of an autonomy supportive, well structured and interpersonally involving teaching style on exercise class participants' psychological need satisfaction, motivational regulations, exercise behaviour, behavioural intention and affect. Female exercise class participants enrolled in a 10-week exercise program were exposed to an SDT-based (i.e. SDTc; n = 25) or typical (i.e. control group; n = 31) teaching style. The control condition reported a significant decrease in autonomy support, amotivation and behavioural intention over time. In addition, they reported a significant increase in competence and introjected regulation. Compared to the control condition, the SDTc reported a significantly greater linear increase in structure and interpersonal involvement, relatedness and competence need satisfaction and positive affect. Attendance rates were significantly higher in the SDTc. SDT-based social-contextual characteristics and psychological needs predicted autonomous regulations; all these variables collectively predicted adaptive outcomes. Copyright © 2007 John Wiley & Sons, Ltd.