A 54-yr-old woman with a pT2pN0 breast cancer developed a long-standing symptomatic breast edema after lumpectomy and radiation therapy. The breast edema did not respond to non-steroidal anti-inflammatory drugs (NSAIDs) and manual lymph drainage of her arm. Three years after completion of radiation therapy, hyperbaric oxygen (HBO2) treatment was initiated. Fifteen HBO2 sessions were performed at a pressure of 240 kPa over 90 min in a multiplace chamber. At the end of treatment, breast discomfort had subsided completely, and 5 mo. after completing HBO2 therapy the patient is still free of complaints. We conclude from this observation that the value of HBO2 in the management of symptomatic radiation-induced breast edema should be investigated in a clinical study, because other effective treatment options are not available for this condition.