The mortality rate due to snakebite envenomation in Costa Rica was estimated from 1952 to 1993. The highest mortality was observed during the 1950s and 1960s, with the highest rate of 4.83 per 100,000 population in 1953. In contrast, a rate of 0.2 per 100,000 population per year was estimated from 1990 to 1993. The most conspicuous decline in mortality occurred after 1970. The highest mortality rates were observed in the provinces of Limón and Puntarenas, especially in regions where tropical rain forests had been transformed into agricultural fields. The lowest mortality was in the province of Guanacaste, where tropical dry forest predominates and Bothrops asper (terciopelo), the most important poisonous snake in the country, is not abundant. The majority of fatalities occurred in the age groups from 10 to 19 years old. Males were more affected than females in a ratio of 3.6:1. Before 1980 most fatal cases did not receive medical attention in hospitals, whereas after 1980 the majority of cases with fatal outcome were attended in hospitals.