A 34-month-old, male, WI/HicksCar rat presented for necropsy as part of a study on aging. Antemortem examination revealed bilaterally symmetrical swelling of both metatarsal regions. On the basis of radiographs, the swelling was determined to be new periosteal bone growth, consistent viith hypertrophic osteopathy. Necropsy confirmed the diagnosis and revealed numerous lesions associated with hypertrophic osteopathy, including congestive heart failure, granulomatous pneumonia, and intrathoracic and extrathoracic neoplasia, Spontaneous hypertrophic osteopathy has not previously been reported in rodents.