The fatal kidnapping of a Japanese macaque infant is described. Kidnapping was followed by a long period (10 weeks) of co-mothering. Quantitative recording showed that both the biological mother (a 8-year-old, low-ranking, multiparous female) and the kidnapper (a 4-year-old, high-ranking female with no maternal experience) displayed an affectionate style of mothering and never responded negatively to the infant's demands for contact. Given the large maternal investment on the part of the kidnapper, we suggest that the fatal outcome for the infant was not the result of reproductive competition. © 1993 Wiley-Liss, Inc.