The results of treating chronic lymphedema using microwave heating are described in 45 patients with postmastectomy lymphedema of the upper extremity. Forty-five patients showed a significant (p < 0.01) reduction in the amount of peripheral edema after two courses of treatment. The incidence and severity of secondary acute inflammation (erysipelas) were also sharply reduced (p < 0.01). The elasticity of the soft tissue was restored.