Abstract Analysis of autopsied cause of death during the London Fog of 1952 indicates that mortality from all respiratory causes, sudden and delayed, had a consistent male fraction of 0.622. Sudden death from heart failure had a similar male fraction of 0.612. However, heart failures after the first day of illness had a male fraction of 0.48. This significant difference in male fraction between sudden (0.61) and delayed (0.48) heart failure suggests different terminal events. Coronary sudden death may be attributable to right-sided heart failure, and the delayed form may be attributable to left-sided failure leading to pulmonary congestion. The male fraction in sudden respiratory and sudden cardiac deaths (0.612) is exactly the same as the male fraction in sudden infant death syndrome - 0.612 - which has been posited as being X-linked. It is hypothesized that the same X-linked gene responsible for the 0.612 male fraction in sudden infant death syndrome may be a factor in the respiratory and sudden cardiac mortalities during the London Fog.