Captive lizards fed a variety of vegetarian and carnivorous diets frequently develop severe nutritional osteodystrophy. Five hatchling iguanas which were captive for 5 months and fed a diet low in calcium and phosphorus developed clinical signs and lesions typical of nutritional osteodystrophy in captive lizards. They had tetany with severe osteoporosis, pathologic fractures, and cartilaginous diaphyseal enlargements of long bones which either were associated with fractures or with intact bones. Hatchling and juvenile iguanas fed a similar diet low in calcium (0.1%) and phosphorus (0.2%) under experimental conditions developed hypocalcemia, tetany, osteoporosis with but adequate in phosphorus (1.1%) developed progressive hypocalcemia and severe osteopososis with pathologic fractures. Control iguanas fed a diet with adequate calcium (2.7%) and phosphours (1.1%) had well mineralized bones with wide cortices and thick metaphyseal trabeculae. Iguanas fed low calcium experimental diets whether low or adequate in phosphorus developed hypocalcemia with compensatory secondary hyperparathyroidism resulting in severe osteodystrophy similar to that reported in captive lizards.