The mitotic chromosomes of 33 species of chelonians representing 22 genera and six families were investigated. Chromosome number and morphology are the same for most members of a given family and range from 66 in Trionyx to 34 in Pelomedusa. Most emydid genera have 50 chromosomes. The karyotype of Chelydra (2n = 52) is similar to those of some testudinid and emydid genera and is unlike the 56 chromosome karyotype of kinosternid turtles. The three genera of tortoises examined, Gopherus, Testudo, and Geochelone, have 52 chromosomes, but Gopherus differs in karyotypic details. The karyotype of Geochelone is like that of Chelydra and the 52 chromosome genera of emydid turtles. The African pleurodiran Pelomedusa has three additional pairs of small acrocentric or telocentric chromosomes not present in the earlier described karyotype of Podocnemis. Examination of meiotic chromosomes revealed frequencies of chiasmata formation similar to those reported earlier. Sex chromosomes were not distinguishable.