The authors reviewed more than 50 studies of qigong therapy for cancer in China, in 3 categories: clinical studies on cancer patients, in vitro studies on laboratory-prepared cancer cells, and in vivo studies on cancer-infected animals. Most of the clinical studies involved observation of cancer patients' self-practice of qigong. Although no double-blind clinical trials were found among patient studies, many had a control. The qigong groups showed more improvement or had a better survival rate than conventional methods alone. In vitro studies report the inhibitory effect of qi emission on cancer growth, and in vivo studies find that qigong-treated groups have significantly reduced tumor growth or longer survival among cancer-infected animals. However, there is much room for improvement in these studies, and some require replication to verify the findings. Qigong therapy is an area that is often neglected by mainstream medicine and research, but our review strongly suggests that qigong deserves further study as a supplement to conventional cancer treatment.