Recent research has applied the theory of planned behavior (TPB) to understanding exercise after a cancer diagnosis, but studies are few and have been limited by retrospective designs, self-report measures of exercise and varied results. In the present study, we extended this research by using a prospective design and an objective measure of exercise adherence. Participants were a convenience sample of 24 breast cancer survivors attending a twice weekly, 12-week training program in preparation for a dragon boat race competition. Participants completed a baseline questionnaire that assessed demographic and medical variables, past exercise, and the TPB (i.e. beliefs, subjective norm, attitude, perceived behavioral control and intention). Program attendance was monitored over a 12-week period by the class instructor. Overall, participants attended 66% of the training sessions. Multiple regression analyses indicated that: (a) intention was the sole determinant of program attendance and explained 35% of the variance; (b) the TPB constructs explained 49% of the variance in intention with subjective norm being the most important determinant; and (c) the key underlying beliefs were support from physician, spouse, and friends, and confidence in being able to attend the training class when having limited time, no one to exercise with, fatigue, and other health problems. Based on this preliminary study, it was concluded that the TPB may provide a good framework on which to base interventions designed to promote exercise in breast cancer survivors. Copyright © 2001 John Wiley & Sons, Ltd.