The giant herbivorous iguanid Ctenosaura similis, of southeastern Mexico and Central America, occurs in open woodland or edge habitat in seasonally dry lowlands. Sexual maturity is attained in the second year, ovulation occurs about mid-February, and laying of the eggs (mean 43.4, 12-88) occurs about 5 weeks later. Hatchlings appear about mid-May and have tripled in length at the end of the first year when they are half-grown in length. Females outnumber males 2 to 1; but males are about 1.25 times female length and 1.8 times female weight. Biomass may be several kg per ha (1.67 per ha on a 10 ha sample area in Belize). Each Ctenosaur centers its activity at a lookout and shelter; typical foraging radii are from 18.8 m in first-year young to 43.0 m in adult males. Food consists of many kinds of foliage, flowers and fruits, and some animal matter including small rodents, lizards, eggs, and insects. Exploitation of the Ctenosaur is heavy in some parts of its range, including Nicaragua, where the species is a common article of diet for country people and also is sold by the hundreds in city markets. As a result, numbers have decreased drastically. Conservation is needed, especially protection of reproductive females, to assure a sustained yield of the flesh, a valuable natural resource.