This study was undertaken to confirm the findings of Naeye with regard to the pathological retention of the so-called brown fat cells in the periadrenal adipose tissue of infants who die of the sudden infant death syndrome. The percent of multilocular fat cells was determined in histological sections of periadrenal adipose tissue obtained from a series of 289 autopsies. In general, our morphological observations confirm his. However, our results indicate that the percent of periadrenal multilocular cells cannot be used as a diagnostic criterion in any single case. Futhermore, we consider that the mechanism for this delay in transformation remains unclear.