BACKGROUND: Exercise is becoming an important component of cancer rehabilitation programs. A consistent finding across studies is that patients experience improved physical fitness and reduced fatigue. However, sustained physical activity is essential if the benefits are to be preserved over the course of cancer survivorship. OBJECTIVE: This study examined self-reported short-term exercise adherence following a 6-week, supervised exercise program (muscle strength, cardiovascular fitness, relaxation, body awareness, and massage) in a heterogeneous group of 61 cancer patients (mean age 42.9 years, 82% oncological and 18% haematological) from the Body & Cancer Project. METHODS: Semistructured interviews were used to quantitatively assess leisure time physical activity level 1 and 3 months after completion of the program. The study furthermore included 3-month follow-up assessment of psychological distress (Hospital Anxiety and Depression Scale-HADS). Patient statements were selected that best illustrated trends found in the statistical material. Results: There was a significant postprogram reduction in physical activity from 6 to 10 weeks and from 6 to 18 weeks. However, the patients (half of whom were still undergoing treatment at the time of follow-up) reported a higher physical activity level postprogram compared to their baseline levels. The analyses showed a positive association between the 3-month postprogram physical activity level and pre-illness physical activity level, treatment, and postprogram changes in depression. SIGNIFICANCE OF RESEARCH: Given the significant decrease in postprogram PA level, especially in subjects still undergoing cancer treatment, the study suggests that continuous supervised programs may be required in order to encourage and support exercise adherence in this population. However, randomized clinical controlled trials and more follow-up studies are needed to establish the optimal program length and content for sustained exercise adherence in cancer patients.