Purpose: To determine if the jitter in the extensor digitorum communis (EDC) muscle in patients with purely ocular myasthenia gravis (OMG) predicts the subsequent development of generalized myasthenic weakness. Methods: Included in this retrospective study were patients who initially had purely ocular manifestations and had been followed for at least 2 years after onset of myasthenic symptoms. The group consisted of 50 patients with purely ocular weakness, 26 of whom later generalized. All underwent single-fiber electromyography (SFEMG) studies in the EDC muscle at the initial examination. Results: Statistical analysis did not demonstrate that the amount of jitter in the EDC muscle predicted the development of generalized myasthenia gravis (GMG). Also, there was no threshold jitter value that predicted generalized weakness. Conclusions: SFEMG measurement of jitter in the EDC muscle demonstrates abnormal neuromuscular transmission in many patients with OMG but is not useful in predicting generalization in these patients. Copyright © 2000 Lippincott Williams & Wilkins, Inc.