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The reproductive cycle of a Population of Sceloporus jarrovii was determined using monthly samples of both sexes collected between April 2004 and March 2005 at the canyon of Las Piedras Encimadas, located in Gomez Palacio, Durango, Mexico. Reproductive activity of both sexes was synchronous, similar to other lizards inhabiting montane zones. Testicular recrudescence began in mid-summer (August), and maximum testicuiar volume Occurred from September to January, declining in February. Testicular recrudescence ill volume was negatively correlated with ambient temperature. Females show fall reproductive activity and the reproductive period extended from November to early May. Vitellogenesis Occurred from mid fall (November) to early winter (January), with ovulation Occurring in late December. Embryonic growth took place from January to May and neonates were observed from May to July.. This fall reproductive pattern is common in females from high elevation Populations of other viviparous Sceloporus. Mean litter size based on embryos in utero was 6.0 +/- 0.32 SE (range 4-8). Litter size was positively correlated with female SVL. Fat body cycles in females and males were similar. Fat bodies in males were largest when maximum reproductive activity Occurred, and decreased after the reproductive season. Females contained large fat bodies from October to January, Followed by a gradual decrease from late winter to mid-spring. Female fat body mass was not depleted until late May, just prior to parturition. This study adds to our understanding of the reproductive cycle of S. jarrovii, and indicates that fall reproductive activity is a common reproductive strategy among viviparous Sceloporus.