Expectancies of cancer patients regarding their physical activity before they took part in a behavior change intervention were compared with their experiences during the intervention period. A total of 66 cancer patients completed either a randomly assigned 4-week physical activity or a stress-management counseling intervention. On average, participants had positive expectancies toward physical activity. Outcome expectancies predicted outcomes (e.g. physical activity) at a 10-week follow-up. Outcome realization (discrepancy between expectancies and experiences) further increased explained variance in self-efficacy and physical activity enjoyment. In conclusion, not only initial outcome expectancies but also their realizations seem to be important for subsequent behavior and cognitions