During December 1, 1996-September 30, 1997, a total of 20,034 cases of measles (incidence: 88.7 per 100,000 population) were reported to the Ministry of Health (MOH) in Romania (Figure 1); 13 cases were fatal. The outbreak began in December 1996, peaked in May 1997, then declined. Cases occurred in the capital (Bucharest) and all 40 other districts (1996 total population: 22.6 million). District-specific attack rates were highest in the northwest and lower in the south, ranging from 10 to 258 cases per 100,000 population. This report describes the investigation of this epidemic by MOH and estimates the efficacy of measles vaccine using the screening method; the findings of the investigation suggest that high routine vaccination coverage with a single dose of measles vaccine with an estimated efficacy of 77%-90% was not sufficient to prevent periodic outbreaks of measles.