This is the first epidemiological study of myasthenia gravis (MG) in the area of Belgrade. During the survey period (1983 1992), 124 incidental cases of MG were observed, producing an average annual incidence rate of 7.1 per million population (women, 8.3; men, 5.8). Age and sex specific incidence rates for females demonstrated a bimodal pattern, with the first peak in the age group between 20 and 40, and the second peak in the age group 70-80. The age-specific rates for males showed unimodal pattern, reaching a maximum in the age group between 60 and 80. There was a tendency of more frequent disease appearance in the urban as opposed to the suburban districts. On the prevalence day, December 31, 1992, the point prevalence rate was 121.5 per million (women, 142.5; men, 98.8). Only for incidental cases, the point prevalence rate was 77.1 (women, 83.2; men, 70.4). The average annual mortality rate was 0.47 per million (females, 0.52; males, 0.42), while cumulative lethality was 5.6 (women, 5.6; men, 5.7). Most frequently initial symptoms were ocular, occurring in 58% patients. Through the period of investigation ocular symptoms were generalized in 68%, most frequently in the first 2 years (62.5%). Thymoma was confirmed in 11.3% of patients. In this group there was equal presence of both sexes, older median age at onset, and more severe clinical course of MG. Associated autoimmune disease was found in 17 out of 124 incidental cases (13.7%). The most common were thyroid diseases (7.3%). Family history of MG was recorded in 2 cases belonging to 1 family (1.6%).