SUMMARY—The anatomy of scrotal fat was studied histologically and by dissection in 28 normal cadavers and 44 idiopathic infertile subjects. Two fat patterns were described: normal and infertile. In the normal pattern, a small posterior extratunicary pad of fat was constantly encountered. lntratunicary fat occurred as small granules between the cord veins.Thirty‐eight of the 44 idiopathic infertile subjects had scrotal lipomatosis, of which 2 types were recognised: extratunicary and intratunicary. The latter showed 2 patterns: diffuse and lobular. The diffuse pattern occurred in obese subjects and those of normal build, and the fat was firmly adherent to the cord veins. The lobular pattern occurred exclusively in the obese, and the lobules were loosely connected to the cord.The anatomical features of the normal fat pattern in relation to maximal testicular thermoregulatory efficiency were discussed. The role of scrotal lipomatosis in infertility was clarified and the relationship of scrotal lipornatosis to obesity presen