The South American iguanian lizard genus Stenocercus includes 58 species occurring mostly in the Andes and adjacent lowland areas from northern Venezuela and Colombia to central Argentina at elevations of 0--4000 m. Limited taxon or character sampling have characterized all previous phylogenetic analyses of Stenocercus, which has repeatedly been proposed as sister taxon to the Tropidurus Group. In this study, I use molecular and morphological data to (1) infer the phylogenetic relationships among most species of Stenocercus, (2) perform explicit statistical tests of previous phylogenetic hypotheses, and (3) infer the ancestral distribution of Stenocercus. Using parsimony and Bayesian analyses, monophyly of this genus is strongly supported with a dataset of 32 species of Stenocercus, 12 outgroup taxa, and 1641 bp of mtDNA. Molecular data also are used to analyze evolutionary relationships within Stenocercus with a Bayesian approach based on mixture models, which accommodate variability in the parameters of the rate matrix across sites. Morphological data were obtained from 55 species of Stenocercus and one outgroup taxon; polymorphic and continuous morphological characters were coded using step matrices with frequency parsimony and gap-weighting methods, respectively. Parsimony and Bayesian analyses were performed with a combined dataset of 55 ingroup taxa, one outgroup taxon, and 1764 characters. All analyses support a basal split of Stenocercus into two clades. When all 55 ingroup taxa are included, these clades are composed of 26 (clade A) and 29 (clade B) species. In general, species in clade A have small scales and granular scales on the posterior surface of thighs, whereas species in clade B have large scales and non-granular, imbricate scales on posterior surface of thighs. Clade A is restricted to the central Andes except for a few species occurring in the northern Andes in Ecuador and Colombia. Clade B is more widespread and includes species occurring in the northern, central, and southern Andes, as well as species in the Amazon Basin and lowlands in southeastern South America. A dispersal-vicariance analysis suggests that the most recent common ancestor of species of Stenocercus occurred in the central Andes. Four new species of Stenocercus are described from the northern Andes of Colombia, southern Andes of Ecuador, northern and central Andes of Peru, and Cerrado forest in Brazil. In addition, S. torquatus is resurrected and S. variabilis is redescribed.