We investigated the importance of ecological and historical effects in structuring a lizard assemblage in a semiarid area of Caatinga habitat. We collected lizards using pitfall traps and active searching; we also collected data concerning microhabitat and diet composition for the lizard species examined. We used null models to test whether or not the community was structured following microhabitat or trophic niches. We also tested whether or not such structure had a historical or ecological origin using canonical phylogenetic ordination and phylogenetic principal component analysis. Gymnodactylus geckoides and Tropidurus hispidus were most generalized in their microhabitat use. Hemidactylus brasilianus and Phyllopezus pollicaris had the greatest numeric niche breadth, whereas P. pollicaris and T. hispidus had the greatest volumetric niche breadth. In contrast, Brasiliscincus heathi and Ameiva ameiva had the smallest numeric and volumetric niche breadths, respectively. The lizard assemblage examined had structure in both microhabitat and trophic niches. We detected phylogenetic conservatism on the basis of spatial niches in the clades Teoidea, Teiidae, and Tropiduridae. In contrast to the predictions of the niche complementarity hypothesis, we found high trophic overlap coupled with low microhabitat overlap for tropidurids. Moreover, spatial niche structure was mainly attributable to historical factors (phylogenetic), whereas ecological factors were more important determinants of trophic niche structure.