Geckos are among the most diverse radiations of lizards; however, the lack of baseline natural history data on the reproductive biology for many species creates a challenge for predicting their long-term persistence. This study aims to fill a gap in our understanding of the reproductive biology of an enigmatic nocturnal gecko endemic to the islands of Curaçao and Bonaire: Gonatodes antillensis. Using radiographs of specimens from natural history collections, we conduct the first investigation of the potential role of endolymphatic sacs in the reproduction of the species. We find that females have larger endolymphatic sacs than males, with further quantification of endolymphatic sac sizes between females with or without visible eggs supporting the hypothesis that calcium stores are built up in the early reproductive phase and depleted during the development of the egg. Additionally, we combined data on endolymphatic sacs sizes with examinations of gravidity to expand the known reproductive interval of the species into fall and winter months and suggest the possibility of year-round reproduction. Along with providing baseline data, our findings raise a new conservation concern for the species. The spread of the invasive gecko Hemidactylus mabouia has resulted in a notable decline in the abundance of Gonatodes antillensis across its native range. This decline has been attributed to Hemidactylus mabouia acting as both a competitor and possible predator of Gonatodes antillensis. However, stress can inhibit calcium uptake in endolymphatic sacs, and these findings raise the possibility that Hemidactylus mabouia may also be indirectly affecting the reproductive success of this species.