Field surveys of butteflies were conducted during 14 months in a Guatemalan dry forest, which yielded 103 species in 79 genera from 18 subfamilies of six families, with Cyanophrys miserabilis (Clench, 1946) (Lycaenidae: Theclinae) as a new country record. A seasonal pattern was shown in which species richness reached a peak at the end of the rainy season and declined greatly in the dry season. Species composition also differed significantly between the two seasons. This is the first quantitative study on the butterfly phenology of a Guatemalan dry forest, which will provide a scientific baseline for future entomological and ecological research and for biodiversity conservation in these forests