A complete autopsy involves correlation of relevant historical facts about the deceased and the circumstances of the death with the external and internal post-mortem findings. Various ancillary tests can assist in the determination of the cause of death. This systematic approach together with an awareness that the pathological changes are subtle or non-specific in certain cases will uncover most inapparent causes. The pathologist must realize that in a small percentage of deaths, the cause will remain unexplained despite extensive investigative efforts. Selected examples are cited to illustrate why a cause of sudden natural or unnatural death can be inapparent. 4 figures and 38 references (Author abstract modified)