A one-year-old neutered male Border collie presented with failure to gain weight, lethargy, intermittent leucopenia, borderline anaemia and intermittent gastrointestinal symptoms. He was diagnosed with pancreatitis based on blood results and abdominal ultrasonography and hereditary selective cobalamin malabsorption based on hypocobalaminaemia, methylmalonic aciduria and genetic testing for cubilin mutation. The dog responded to oral cobalamin supplementation with resolution of clinical signs and normalisation of serum cobalamin. There was no recurrence of signs after 27 months of follow-up. An association between organic acidaemias and pancreatitis has been reported in humans but to the authors' knowledge, this is the first report of hereditary selective cobalamin malabsorption and concurrent pancreatitis in a dog. Furthermore, this is the first report of inherited canine cobalamin deficiency responding to oral cobalamin supplementation.