Vitamin B12 (cobalamin) deficiency is recognized as an etiology of bladder dysfunction but there are few detailed descriptions of such cases. We report on a woman with weakness and sensory ataxia from neuropathy in whom a sensory neurogenic bladder developed. Thorough investigation revealed no cause for bladder dysfunction other than deficiency of vitamin B12, supported by elevated levels of methylmalonic acid and homocysteine. The addition of our case to those previously reported may aid in the earlier recognition and treatment of this syndrome.