To investigate risk factors of unintentional carbon monoxide deaths in California from nonvehicular sources, we identified 270 deaths resulting from nonvehicular sources of carbon monoxide poisoning from death certificates and coroners' investigation reports. Data recorded between 1979 and 1988 in the state of California on risk factors and carbon monoxide sources were abstracted from investigation reports. We also used census and state statistics to calculate rates and relative risks. The highest rates, which occurred in winter, were found among males, African Americans, and the elderly. Relative risks (in parentheses) were higher among individuals who (a) lived in multiunit dwellings (2.1), (b) dwelled in mobile/trailer homes (4.7), and (c) resided in temporary shelters (30.0) than among individuals who lived in single-family houses (1.0). Unvented combustion heating appliances and charcoal fuel were associated significantly with the risks of fatal unintentional carbon monoxide poisoning.