Acute hemorrhagic conjunctivitis due to enterovirus 70 has caused extensive outbreaks in tropical areas since 1969. Between December 1, 1990, and March 4, 1991, an outbreak of acute hemorrhagic conjunctivitis due to enterovirus 70 occurred in American Samoa, where an outbreak due to the same agent had occurred in 1981. A survey of 5% of the households (134 households, 1,095 individuals) was conducted throughout the island of Tutuila. The outbreak affected 58% of the population, with age-specific attack rates greater than 50% for all age groups except children younger than 2 years. Attack rates were significantly higher for children 2-10 years old (65%) than in the remainder of the population. Women aged 21-40 years had higher rates than did men the same age (66 vs. 49%), possibly because of the close association of women and young children. At higher preepidemic titers, there was evidence of protection from clinical disease among males but not among females. Enterovirus 70 can cause large outbreaks even in a population already exposed in a previous large outbreak; protection due to previous infection is only partial.