Twenty-six patients with proven myasthenia gravis were interviewed to assess the length of time between onset of symptoms, presentation to the general practitioner and diagnosis. In one third the initial diagnosis was psychiatric and the average time between presentation and correct diagnosis was 2.8 years for men, 1.2 years for premenopausal women and three weeks for postmenopausal women. Diagnosis could have been made much earlier if doctors had been familiar with early symptoms in this relatively rare disease. Symptoms and signs fluctuated and were at times absent, especially in the mornings.