Reindeer (Rangifer tarandus) living on the subantarctic island of South Georgia were found to have a high prevalence of dental abnormalities and mandibular swellings (11 to 30 per cent, and 9 to 19 per cent, of adults and yearlings, respectively). Soft tissue examination and radiography suggested the swellings were “lumpy jaw”, but actinomycotic organisms were not cultured. Fluorine levels in affected mandibles were low (50 to 400 ppm). Normal mandibles hadl ow volumetric and radiographic compact bone percentages; those from affected mandibles were significantly lower and there was radiographic evidence of osteoporosis. It is suggested that the high incidence of mandibular and dental lesions (compared with northern populations of Rangifer) results from the environmental peculiarities of South Georgia.