A field study on two populations of the tropical iguanid lizard Plica plica in the Brazilian Amazon revealed that this lowland forest species is diurnal, occurs on vertical smooth-barked trunks of the largest trees in the forest, and feeds mostly on ants. Comparisons between rainy season samples from Pará and dry season samples from Rondonia show that even though lizards ate, on average, the same number of prey, prey were larger in Rondonia and prey diversity was greater in Pará. Lizards sleep on tree trunks or similar surfaces when available, apparently leaving the trees only to deposit eggs. Clutches are deposited in palm litter and inside rotted palm trunks. Clutch size averages 2.9 ± 0.1 eggs and is significantly correlated with female snout–vent length. The reproductive season appears to be extended in that females produce at least two clutches. Relative clutch mass of females is low compared with that of other sit-and-wait foraging lizard species, and this, coupled with the flattened morphology, presumably reflects adaptations for maintaining the center of gravity near vertical smooth tree trunks.