We report the case of a patient with a history of an atypical lung carcinoid tumor who developed a rapidly progressive memory impairment. The clinical presentation as well as brain MRI, cerebrospinal fluid, and laboratory tests led to the diagnosis of seronegative paraneoplastic autoimmune limbic encephalitis. To the best of our knowledge, this is the first case in literature of such association. This case also highlights an exceptionally favorable outcome, both clinically and radiologically, after immunosuppression and tumor removal.