A survey of the aetiological agents and clinical aspects of an outbreak of acute hemorrhagic conjuctivitis (AHO in Cuiabá, MT, Brazil, that occurred between December 1982 and February 1983 was performed. Neutralization and complement fixation tests were done on 28 paired serum samples, using enterovirus type 70 (EV 70) and adenovirus. Serological conversions for EV 70 were found in 89,3% (25 patients). Aproximately 70% of the population had conjunctivitis, but no neurological complications were observed among patients during or after the outbreak.