Fat necrosis was present in 22 of 400 cases of consecutive postperinatal mortalities investigated to assess the presence and pattern of deep fat necrosis. In just over 50% of the cases of fat necrosis the cause of death was categorised as sudden infant death syndrome, which also showed more severe degrees of necrosis. The mechanism of necrosis may be vascular hypoperfusion, possibly related to shock, and brown adipose tissue, on account of its high metabolic activity and rich capillary plexus, may be particularly vulnerable to infarction. The occurrence of fat necrosis in association with other causes of death did not provide any definite clue as to the nature of the alleged shock.