Lipoma is one of the unusual benign breast neoplasms and usually manifests at fatty breast of women at the age of 40 to 60. We experienced a case of large breast lipoma nearly replacing the whole left breast parenchymal tissue with mammographic finding of well-defined radiolucent mass, sonographic finding of hyperechoic mass with disorganized echopattern and computerized tomographic finding of very low attenuation mass, characteristic to adipose tissue, in a young woman of her dense breast.