The morphology of hemipenes, the male external genitalia of reptiles, is considered to be a character of taxonomic importance. It has, however, until recently been used only rarely in agamid systematics. Phylogenies of Sri Lankan Agamidae, constructed using mitochondrial DNA and hemipeneal morphology, have shown remarkable convergence, highlighting the importance of hemipeneal morphology in the taxonomy of these lizards. Here we present descriptions and illustrations of the hemipenes of 17 of the 18 species of Sri Lankan Agamidae and provide a key to the identification of species groups based on this character. Ceylon Journal of Science (Bio. Sci.) 41 (2): 111-123, 2012 DOI: http://dx.doi.org/10.4038/cjsbs.v41i2.5381