Beetle genitalia are usually described only for taxonomic purposes without considering the possible function of structures. Exceptions are sporadic detailed studies on single species. We studied genital structures in the subfamilies of Cerambycidae and outlined assumptions on the function of these structures and the implications for the phylogeny of the Cerambycidae. We found that male genitalia in particular are taxon-specific on a higher taxonomic level; e.g., the parameres are widely variable in Cerambycinae, while in most Lamiinae species they appear relatively uniform and differ from those of the Cerambycinae. Internal sac structures are very different among the various subfamilies. Small backwards-pointing spines are the most common armature of the internal sac. The female genitalia are less variable, although ovipositor morphology may differ among subfamilies. In most species, the connection between the mates during copulation is achieved by the long internal sac and the ovipositor only, whereas the median lobe and parameres are in contact with the female abdomen only at the beginning of copulation. Cerambycinae and Lepturinae have a basal swelling of the endophallus to prevent it from sliding back into the male abdomen during copulation. The long internal sac functions in connecting the mates and guaranteeing the sperm transfer.