The historic rarity of the critically endangered Grand Cayman blue iguana, Cyclura lewisi, has prevented detailed research on this species prior to this decade. This study primarily used focal animal observations, transect sweeps, and radio-telemetry to document the behavioral ecology of a captive-bred, reintroduced population of adult C. lewisi in a botanic park on Grand Cayman. Activity budgets and foraging budgets are presented for each sex in each season, and for all data combined. Distributions of basking time and active time differed between the two seasons. Iguanas both emerged earlier and retreated later in the summer than in the fall. Of the small percentage of time spent active, iguanas mostly foraged and engaged in locomotion. Iguanas spent little time in trees or bushes or inside of retreats during the day. Observations of extensive tongue-touching of retreats, substrates, and feces suggest an importance of chemosensory ability in C. lewisi. Iguanas primarily consumed plant matter, of which the majority was non-cultivated plants in the park and surrounding area. Limited geophagy, coprophagy, and consumption of invertebrates were observed. Supplemental feeding contributed little to the overall diet of iguanas, but appeared to make iguanas more aggressive towards humans. Iguanas were heavily habituated to human and vehicular disturbances, which were common occurrences. Aspects of the behavioral ecology of C. lewisi reported here will assist in the conservation of this and other endangered iguanas.