Qigong is an exercise involved deep breathing, concentration, and relaxation techniques used by individuals for themselves. Qigong had been incorporated into Chinese medicine for very long time.
In Chinese Medicine, there is only one cause of illness and that is congestion. When Qi (vital energy) is blocked within the body system, the Yin and Yang become imbalance, then the body eventually manifests some physical imbalance or sickness. Qigong, like other practical methods as acupuncture, tuina etc, can influence the flow of vital energy and naturally help relieve congestion and therefore, is beneficial to health.
Some Qigong masters claimed that they had cured a wide variety of diseases including cancer, heart disease, AIDS, arthritis, and asthma etc. Unfortunately, until now, there are no large, scientifically organized clinical trials to support these claims. Therefore, although Qigong can undoubtedly improve fitness and general well-being, there's no reason to believe that it will cure any serious disease.