The reproductive activity of most of tropical Andean snakes is unknown, especially for fossorial species. An undescribed species of Atractus from Cordillera Oriental of Colombia occupies a habitat that undergoes two rainy seasons and two dry seasons. This strongly seasonal climate suggests that the reproductive phenology of the species might be seasonal or continuous with reproductive peaks related to rainfall. To test this hypothesis, we studied the annual reproductive activity of this population and other aspects of its reproductive biology. We determined the reproductive stages in males by studying morphometry and histology of the testes, sexual segment of the kidney (SSK), and excurrent ducts. In females, reproductive stages were based on the macroscopic and morphometric analyses of the ovaries and histology of the oviducts. Adult males had spermatozoa in testes and ducts and hypertrophied SSK throughout the year. Similarly, reproductive (vitellogenic) females were found during most of the year; however, a high percentage of adult non-reproductive females (44%) was also found throughout the year. Therefore, females are asynchronous in their reproductive stage. Similarly, juveniles of different sizes were found year-round and no particular time of neonatal recruitment was detected. All adult females had abundant sperm within crypts, the lumen of the vagina, and the utero-vaginal junction, suggesting extended or permanent female receptivity. In contrast, although all females had seminal receptacles in the posterior infundibulum, only late vitellogenic females had sperm within these receptacles, suggesting preovulation migration of sperm from vaginal crypts to seminal receptacles. Therefore, adult males are reproductive throughout the year and constitute a permanent resource for females, whereas females have extended, aseasonal reproductive cycles with an evidently discontinuous reproductive cycle with only one clutch per year.