Three epidemics associated with Mayaro virus have been described in the literature: two in Brazil, and one in Bolivia. The first reported epidemic occurred in 1955 in a community of quarry and forest workers on the Guama River, 120 miles east of Belem in the Amazon region of Brazil. The epidemic in Bolivia was also seen in 1955, and affected a community of some 400 Okinawan workers who had recently colonized a forested area east of the Rio Grande, Bolivia. The third reported outbreak occurred in the first half of 1978 and affected the village of Belterra, which is situated near the confluence of the Tapajos and Amazon Rivers, Para State, Brazil. A total of 55 cases were confirmed, by virus isolation and serology, and 12 by serology only. Although no fatalities due to Mayaro virus infection have been documented, there is evidence suggesting that this disease may cause a significant morbidity among rural populations.