The planthopper Poekilloptera phalaenoides (L.) (Hemiptera: Flatidae) is a very common species in various regions of Brazil. The aim of this study was to report on P. phalaenoides biology, its behavior, and host plants in agricultural and natural vegetation areas of the Brazilian Cerrado and to relate the bio-ecology of this species with the climatic characteristics of the biome. The study was conducted between 2005 and 2008 in agricultural areas, and areas covered with typical cerrado sensu stricto and cerradão phytophysiognomies (Planaltina, Federal District, Brazil). Weekly field samples were taken to observe the biological stages of P. phalaenoides. Adult population dynamics were studied using light traps. Host plants were observed in natural vegetation areas. P. phalaenoides presented an 11-mo life cycle (egg to adult). The egg stage, which undergoes diapause, lasted ∼6 mo, and the nymphal stage lasted 7 mo. Adults were most abundantly found in October (64.7%). Specimens of P. phalaenoides were observed on nine species of plants; however, all the biological stages were observed only in Maprounea guianensis Aublet, Sclerolobium paniculatum Vogel, and Salacia crassifolia (von Martius) Peyr. Our results suggest that the life cycle and behavior of P. phalaenoides are synchronized with the climatic conditions of the Brazilian Cerrado, with adults present during the rainy season, when oviposition sites are more available, and the immature stages present in the dry season, when they can benefit from lower interspecific competition and a lower incidence of natural enemies. This is the first bio-ecological study conducted on a representative of the Flatidae family in Brazil.