In 1998 we determined in vivo and in vitro the frequency and the degree of resistance of Plasmodium falciparum to the three antimalarials (chloroquine, amodiaquine, and sulfadoxine/pyrimethamine) most utilized in the municipality of Turbo (in the area of Urabá, Antioquia, Colombia), in a sample representative of the population with malaria. We carried out clinical and parasitological analyses over a 14-day period using the standard test recommended by the World Health Organization. In vivo, P. falciparum showed resistance to chloroquine, amodiaquine, and sulfadoxine/pyrimethamine, with a frequency of 97%, 7%, and 13%, respectively. In vitro, the corresponding figures were 21%, 23%, and 9%, respectively. For chloroquine the level of agreement between the in vivo and in vitro results was 23%.