A 54 year old woman with auto-immune hepatitis on treatment with azathioprine for five years who presented with sub-acute neurologic symptoms of right facial drooping and loss of vision in the right eye. MRI revealed a ring-enhancing pontine lesion. Pathological examination proved this to be large B-cell primary central nervous system lymphoma (PCNSL). The imaging characteristics of the tumor were that of a ring-enhancing mass typical of PCNSL found in HIV patients.