Diffuse skin thickening of the breast is produced by lymphedema usually secondary to obstruction of theaxillary lymphatics. On physical examination, the affected breast is, due to increased fluid content, larger,heavier, and of higher overall density. Mammography reveals an increased coarse reticular pattern. Thickening ofthe skin can have many causes. It may be a result of tumor invasion or a tumor in the dermal lymphatics; orbecause of lymphatic congestion through obstruction of lymphatic drainage within the breast, in the axilla, orcentrally in the mediastinum. Further causes may be congestive heart failure, benign inflammation, primary skinprocesses such as psoriasis, or systemic diseases which involve the skin. Mammographic appearance is known to benonspecific. Ultrasound can demonstrate skin thickening directly, but despite some reports suggesting that thecause of skin thickening can be inferred from the results of ultrasound, this is not usually of practicalimportance. The purpose of this study is to review the causes of skin thickening of the breast and to usemammography and US to differentiate the causes.