Myasthenia Gravis is a chronic autoimmune neuromuscular disorder that is characterized by fluctuating weakness of the voluntary muscle groups. It occurs in all races, at any age (especially under 40 or over 60), both genders, with a prevalence of 20/100,000 population in the United States. About 15 percent of patients with myasthenia gravis have thymomas, much rarely another solid tumor, thyroid dysfunction and more often another autoimmune condition, such as rheumatoid arthritis, lupus, Biermer anaemia. We present a 72 year-old male patient with ocular myasthenia gravis treated with cholinesterase inhibitors, that, after many laboratory exams, was diagnosed with acute erythroblastic leukemia, a very rare clinical association.