Facial abscesses in a colony of common marmosets were found to be caused by abscessation of an upper canine tooth root. Trauma to the upper canine, resulting in exposure of the pulp cavity, was thought to be the mode of infection. Radiography was the most useful diagnostic aid in establishing the nature and extent of the lesion. Antibiotic therapy alone was inadequate, and provision of drainage by extracting the tooth, in conjunction with antibiotics, proved the most effective treatment.