OBJECTIVES: Supervised exercise is beneficial for lymphoma patients, but it needs to be maintained to optimize long-term benefits. Here, we report the predictors of follow-up exercise behavior 6 months after a randomized controlled trial in lymphoma patients. METHODS: Lymphoma patients were randomly assigned to 12 weeks of supervised aerobic exercise (n = 60) or usual care (n = 62). At baseline and post-intervention, data were collected on demographic, medical, health-related fitness, quality of life, and motivational variables. At 6-month follow-up, participants were mailed a questionnaire that assessed exercise behavior and were categorized as meeting or not meeting public health exercise guidelines. RESULTS: At 6-month follow-up, 110 participants (90.2%) responded, of which 61 (55.5%) were meeting public health exercise guidelines. In univariate analyses, 16 variables predicted 6-month follow-up exercise behavior. In a stepwise regression analysis, five variables entered the model and explained 38% (p < 0.001) of the variance including the following: accepting a post-intervention exercise prescription (β = 0.33; p < 0.001), achieving a higher peak power output at post-intervention (β = 0.28; p = 0.001), experiencing a larger positive change in perceived behavioral control (β = 0.18; p = 0.028), having Hodgkin lymphoma (β = 0.19; p = 0.025), and having a stronger post-intervention intention (β = 0.18; p = 0.034). CONCLUSION: Exercise behavior in lymphoma patients 6 months after a randomized trial was predicted by a wide range of demographic, medical, health-related fitness, quality of life, and motivational variables. These findings may help facilitate the uptake of self-directed exercise after short-term supervised exercise in lymphoma patients.