A relatively new development to the milieu of archaeological techniques routinely used in the Pacific Island region, the stable isotope analysis of human skeletal and dental remains has provided important insights into diet, methods of subsistence and also intra-population variation in diet that may be related to age, sex or status. This study is a stable isotope analysis of one of the largest skeletal samples discovered in the Pacific Islands, from the Namu burial ground (ca. 700–300 bp) located on the small island of Taumako, Southeast Solomon Islands. Here, the stable isotope ratios of carbon and nitrogen of bone collagen (n = 142, δ13Cbone and δ15Nbone) and tooth dentine (n = 86, δ13Ctooth and δ15Ntooth) are analysed to assess adult (survivor) and subadult (non-survivor) diets and patterns of breastfeeding, which also provided insight into possible maternal and foetal/perinatal stress in the population. The δ13Cbone and δ15Nbone results suggested that the adolescents and juveniles who died were eating foods from lower trophic levels than those who survived to adulthood, especially the males. The δ13Ctooth and δ15Ntooth stable isotope values suggested that, during the ages of 5–9 years, individuals were eating more terrestrial and less marine foods than later in life as adults. The sex differences in adult diet (δ13Cbone and δ15Nbone values) were not present as children (δ13Ctooth and δ15Ntooth values). The intra-population variation is discussed in the context of wider Pacific island diet and cultural processes and recent developments in understanding stress and disease processes on human stable isotope values.