A retrospective study of neoplasia in reptiles held at the Philadelphia Zoological Garden was conducted. A total of 3,684 original necropsy reports for the period 1901–2002 were reviewed and revealed 86 cases of neoplasia. Original glass slides or re-cuts from paraffin-embedded tissue blocks were examined for confirmation of the original diagnosis. At necropsy, a total of six neoplasms were identified in six of 490 chelonians (1.2%), 22 neoplasms in 19 of 736 lizards (3.0%), and 58 neoplasms in 53 of 1,835 snakes (2.9%). An additional 12 neoplasms were found in biopsies of one turtle and 10 snakes. In the chelonians, all the neoplasms were seen in turtles, four of six tumors were malignant (66%) and no organ predilection was noted. For lizards, the liver was the most commonly affected organ, with 7 of 22 primary neoplasms (31%). Multiple tumor types were identified in three lizards (15%), metastasis occurred in five cases (25%), and malignant tumors were identified in 16 cases (73%). In snakes, the liver was most frequently affected by neoplasia at necropsy, with 13 of 58 primary neoplasms (22%); multiple types of neoplasm were identified in five cases (10%) and metastasis in six (9%); and 42 tumors (80%) were diagnosed as malignant. When biopsies were included for snakes, however, the skin was the most commonly affected organ, with 17 of 69 neoplasms (24%). One of five lizards (20%) and four of six snakes (66%) with metastasis also had a second primary neoplasm. Since 1967, the incidence of lizard neoplasia has increased from 0.7% to 5.9%, and snake neoplasia has increased from 2.6% to 9.3%.