Characteristics of 305 calving sites used by 131 different radio-collared caribou (Rangifer tarandus) cows from the Porcupine herd in northeastern Alaska and the northern Yukon Territory were investigated between 1983 and 1990 to determine the factors influencing calving site selection. Cows selected areas north of the foothills primarily to reduce exposure of calves to predators. Sites dominated by Eriophorum tussocks were selected secondarily for access to newly emerging vegetation. Highest calf mortality occurred in years when snowmelt was relatively late and calving occurred closer to the foothills and in Canada. Industrial development of the coastal plain of the Arctic National Wildlife Refuge could increase calf mortality if calving were displaced south and east of potential development areas.