Neuromyelitis optica spectrum disorders (NMOSD) and myasthenia gravis (MG) are disorders that affect the central nervous system and the neuromuscular junction respectively. Although both conditions are rare, reports of the coexistence of these two pathologies are increasing worldwide. Rarely, patients with MG develop aggressive forms of neuromyelitis optica (NMO) after thymectomy. Here, we describe two Peruvian patients with the association of MG and NMO.