This comprehensive study of organ weights in sudden infant death syndrome (SIDS) should be of use to those studying postmortem data in SIDS and may have application to issues of growth and development. Analysis of data from 500 autopsies, performed over 15 years by one individual, revealed mean body weights generally below the 50th percentile for living infants. The weights of the thymus, lungs, liver, and brain were significantly greater than published norms. Thymic weights in SIDS probably represent the normal state more closely than those reported in several other series; elevated lung weights are presumably due to the intense pulmonary congestion and edema commonly encountered in SIDS; the liver edge routinely extends below the costal margins at SIDS autopsies, but the reason for increased weight is unknown, although a hemodynamic alteration seems likely; elevated brain weight has been described previously in SIDS. Other organs showed trends differing from "normal"--heart weights showed a marginally significant increase above published norms; for the adrenal glands, a uniform decrease was apparent, but slopes of linear regressions were low, hampering statistical analysis. Organ weights correlated more closely with body weight than with age. When victims were classified as "possible SIDS," "probable SIDS," or "classic SIDS," differences in organ weights were rarely significant. Analysis of organ weights using Z scores and their standard deviations (sigma-Z, or "pattern variability index") revealed increased variability in SIDS victims. Explanations for these findings include the possibility that some weights previously published as normal are low due to confounding variables. Changes could also be genuine, resulting from disturbances in growth or physiology, or artifactual, possibly the result of agonal or postmortem changes. A database on carefully selected, previously healthy infants who died suddenly and unexpectedly of known causes (i.e., trauma) is much needed.