Myasthenia gravis (MG) is an antigen-specific autoimmune disease in which antibodies directed against nicotinic acetylcholine receptors of the postsynaptic muscle membrane (nAChR) impair neuromuscular transmission. MG is clinically characterized by abnormal muscle fatigue and weakness. The initial symptoms and signs are often unrecognized. Therefore, we analyzed the diagnostic errors and duration of diagnostic delay in patients affected with MG (n = 444) in a ten-year period (January 1, 1983-December 31, 1992) in Yugoslavia. The initial diagnosis was correct in 44.4% of patients and erroneous in 38.4%; 17.2% of patients were admitted without an initial diagnosis. The average duration of diagnostic delay was 11 months. We present the differential diagnostic difficulties in MG and discuss the principles of diagnostic strategy which may reduce the risk of diagnostic errors in MG.