A 2 year old intact male guinea pig presented to the Cornell University Hospital for Animals Emergency Service on July 12, 2008 for the acute inability to open his mouth as well as severe jaw pain. CT scan of the patient’s skull revealed a severely thickened and sclerotic left tympanic bulla with concurrent periosteal reaction and bony proliferation of the temporal and parietal bones. This lesion extended into the left temporomandibular joint leading to complete destruction of the joint. The patient was presumptively diagnosed with bulla osteitis and an infection of the temporomandibular joint, which caused mal-alignment of the jaw and subsequent chronic dental disease. Due to the extensive nature and close proximity to the brain, the lesion was deemed inoperable. Treatment consisted of frequent dental trimmings, syringe feeding, pain medications and antibiotics as needed for infection.