PURPOSE: To assess the clinical characteristics of the 2000-2001 measles outbreak in the Seoul metropolitan area, Korea, the clinical data of measles inpatients were analyzed. METHODS: Three hundred and five children diagnosed with measles by clinical manifestation from July, 2000 to February, 2001, in Seoul, Ilsan and Ansan City were grouped according to their age and investigated for clinical manifestations, vaccination history and measles-specific IgM/IgG antibody positivity. RESULTS: Thirty eight point seven percent of the subjects were less than 12 months of age, 27.5 % were 12-47 months of age and 33.8% were 48 months of age or older. There was no significant sexual difference(male : female=1.2 : 1). This epidemic started in June, 2000 and the number of patients increased abruptly in October, peaked in December and finally decreased after February, 2001. It started from the older age group and moved to the younger. Sixty five point two percent had a history of more than 1-dose vaccination and 13.6% of the patients equal or more than 48 months of age had a history of 2-dose vaccination. Primary vaccine failure rate was 59.4%(107/ 180) and secondary vaccine failure rate was 3.9%(7/180) in 1 dose vaccinees. Sixty one point six percent showed more than one complication and 38.4% had no complication. The most common complication was pneumonia(31.8 %), followed by bronchitis(11.5%) and acute otitis media(4.6%). Vaccination and dose were not related significantly with the occurrence of complications. CONCLUSION: Compared with previous outbreaks in Korea, clinical features showed no specific change in the 2000-2001 measles epidemic. However, primary vaccine failure rate was so high that the second vaccination at four to six years of age must be emphasized in Korea.