Mesenrhombencephalitis is a rare inflammatory process involving the midbrain, pons, and medulla. The diagnosis is difficult as clinical and laboratory findings may be nonspecific. Magnetic resonance (MR) imaging demonstrates abnormal T2 signal in the brainstem, which can suggest the diagnosis. The clinical, laboratory and MR imaging findings are described in five patients with this serious, life-threatening disease. MR imaging can be of value in the early diagnosis of this rare disorder.