This is the first of a series of studies on puerperal fatality, which is defined as the risk of death to the mother associated with the delivery of a viable live birth or stillbirth. The studies are based on over a quarter of a million deliveries and nearly 700 maternal deaths which occurred in New York State (exclusive of New York City) in the 3-year period 1936-38. The information was obtained from routine vital statistics records of births and deaths by a process of matching the maternal death certificate with the birth or stillbirth certificate of the infants. The avg. interval between birth of child and death of mother was 9.1 days. The 1st 24 hrs. after delivery accounted for 37% of all maternal deaths. The puerperal fatality rate was 19.3 per 10,000 deliveries when the infant was born alive, and 298.7 when the infant was born dead. The rate was 16.6 for mothers whose infants survived the neonatal period and 108.0 for mothers whose infants died under one month of age. The stillbirth rate was 27.0 per 1,000 total births for infants of surviving mothers and 300.4 for infants whose mothers died in stillbirth. The puerperal fatality rate was 20.1 when birth was at term and 141.3 when it was premature. No difference was noted in the puerperal fatality rate by sex of infant. The rates of loss for both mother and infant associated with plural births were 3 times as high as the rates for single births. Unwed mothers who were delivered of viable offspring had the same puerperal fatality rate as married mothers. The rates of loss for both mother and infant were the same whether the mother resided in an urban locality or in a rural district.