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The reproductive cycle of an introduced population of the brown anole, Anolis sagrei, from O'ahu, Hawai'i, was studied from a histological examination of monthly samples collected July 1999 to June 2000. Males undergo a seasonal testicular cycle in which all males > 38 mm snout-vent length are in spermiogenesis from January to August. Although some ovarian activity was found in all months, the period of greatest ovarian inactivity was October- December, which corresponds to the time of male gonadal regression. The reproductive cycle of A. sagrei in Hawai'i resembles that of populations in Belize, Florida, and Jamaica, where minimum gonadal activity was recorded from November through February. Body sizes at reproductive maturity were similar in all four localities. Anolis sagrei in Hawai'i has an ovarian cycle typical of other Anolis lizards with a prolonged breeding season and production of single eggs in succession. Because A. sagrei has been in Hawai'i for only approximately 20 yr, sufficient time has not elapsed to allow evolution of its reproductive cycles, but this study presents baseline reproductive data that can be used for future studies to see if the A. sagrei reproductive cycles are modified as the lizards adapt to the environmental conditions of their newly colonized range.