We report the clinical and laboratory characteristics of measles infection in an unselected group of 461 young adults. Otitis media was diagnosed in 9.8%, sinusitis in 4.1%, pneumonia in 3.7%, and keratitis in 3.3% of the patients. Minor T-wave changes on electrocardiogram were observed in only 0.7% and jaundice in 0.4%. Elevated liver enzymes were found in 51% of the patients. Creatine kinase (CK) MM fraction was high in 44%. Traces of myoglobin were found in the urine of 14% of those with a high CK, and of the 13 patients with the higher CKs, 12 had an abnormal serum aldolase. We emphasize several points of interest in this large and unselected group of young adults. There was 1) possible evidence of rhabdomyolisis in some of our patients; 2) a lower rate of electrocardiogram abnormalities than previously reported; 3) no evident correlation between initial laboratory values and subsequent complications; and 4) lack of a clinical or laboratory difference between patients who had been vaccinated with an attenuated virus during childhood and those who had not.