Steatocystoma multiplex, a cutaneous disorder involving the appearance of sebaceous cysts on the trunk and upper arms, is often inherited as an autosomal dominant trait. The authors present mammographic and US findings of steatocystoma multiplex in a 35-year-old woman with breast masses. On mammograms, multiple uniform thin walled round or oval shaped oil cysts were seen in the peripheral portion of the breasts and axilla, and on US, well-defined or smooth ill-defined round or oval shaped nodules were seen in the subcutaneous layer of the breasts and axilla; compared with subcutaneous fat, there was iso- or slightly increased echogenicity.