BackgroundThere is increasing evidence showing beneficial effects of mindfulness and mindfulness training on various indicators of mental and physical health. Purpose This paper reports the 6-month follow-up effects of a mindfulness stress reduction training program among patients treated for cancer on perceived stress, depression, anxiety, post-traumatic stress symptoms, positive states of mind, coping self-efficacy, and mindfulness. Methods Patients with a previous cancer diagnosis were recruited and randomized into an intervention group or a waiting-list control group. The intervention consisted of an 8-week mindfulness-training course. Results Compared to participants in the control group, the intervention group showed a larger increase in mindfulness at 6-month follow-up. However, there were no differences on any of the other outcomes between the intervention and control groups. Continued meditation practice was associated with a significant reduction in post traumatic stress symptoms of avoidance. Conclusions The study draws attention to the need to better understand the mechanisms behind the effect of mindfulness training, and to potential modification of mindfulness interventions to promote sustained benefits over time.