The Mexican Revolution was a demographic disaster, but there is little agreement about the human cost or its demographic components. Were the missing millions due to war deaths, epidemics, emigration, lost births, or simply census error or evasion? Reading the demographic history of the Revolution from a subsequent census, such as the highly regarded enumeration of 1930, yields more precise figures than those obtained from the usual benchmark, the census of 1921. The 1930 figures are of better quality and, therefore, more suitable for making an assessment by age and sex. This analysis shows that in terms of lives lost, the Mexican Revolution was a demographic catastrophe, comparable to the Spanish Civil War, which has been ranked the ninth deadliest international conflict over the past two centuries.