Among the 19 currently recognized species of Sminthopsis, differences in the morphology of the free portion of the penis can be seen in the tip, which may be bifid, blunt, knoblike, or have a terminal median process, and which may have a subterminal skin fold; and the urethral opening and terminal passage (urethral grooves or urethral chamber). The urethra may open dorsally or ventrally, and the urethral grooves may lie mesially or ventrally on the bifid portion of the tip. Ten forms can be recognized and interspecific affinities based on penis morphology have been examined for congruence with species groupings based on other independent character sets including external, cranial, and dental characters and molecular data. Penis forms showed the greatest congruence with phylogenetic groups delineated by molecular data.