The Natural History Museum, London (NHM) houses one of the largest archival collections of NBW skeletal specimens in the world. The goal of this research project was to collect samples from the museum’s NBW specimens for bulk stable isotope (δ13C or δ15N) analysis. Similar to most museum cetacean collections, NBW specimens at the NHM were largely gathered from beach cast or stranded animals, and given NBW size, the collection reflects a geographic emphasis on animals found locally, across the species’ eastern North Atlantic range. This is the first open access stable isotope reference data set published for NBW of the northeastern Atlantic, with considerable temporal scope (1845–2006; but see also MacLeod 2005). This reference dataset is contributing to ongoing geographic and tissue specific comparisons with other stable isotope datasets for NBW and other species of cetaceans. Stable isotope data can also be used to support interpretation of the provenance and life history of NBW specimens in the NHM’s significant cetacean collection. NHM register numbers of specimens sampled are recorded in the attached data.