This paper reviews deaths in which there is an environment that is low in oxygen and/or has elevated levels of carbon dioxide. These deaths present problems to autopsy pathologists, as the autopsy is typically negative and postmortem toxicology cannot be used to detect the effects of hypoxia and raised levels of carbon dioxide. Deaths from hypoxia and raised carbon dioxide may be encountered in work-and nonwork-related environments. Typically these are accidents, but suicides may be encountered and criminal charges may follow these events. Environments that have been associated with these events include mines, tunnels, sewers, and pits. Transportation incidents may also be associated with hypoxic events, particularly aircraft and submarines. When an atmosphere low in oxygen is entered, collapse can be rapid, or immediate if the environmental oxygen is below 6%. Environments rich in carbon dioxide can also cause death, even with a high oxygen concentration. Such environments may be encountered in industrial settings, but also occur in natural disasters such as the Lake Nyos disaster. The identification of these deaths typically requires a coordinated investigation with safety inspectors and other experts in industrial- and work-related deaths.