The reproductive characteristics of trogloxenicGoniosoma spelaeumwere studied directly in the field in caves of the Ribeira River Speleological Province, São Paulo State, south-eastern Brazil. They reproduce throughout the year, with one marked peak during the rainy season and a second minor peak in the dry season. During copulation, the male grasps the female pedipalps with his pedidalps, and the pair keep a face-to-face position. After mating, the male stays close to the female, waving his second legs over her body while she proceeds with egg-laying. Each group contains ca. 60–80 eggs of 2.1–2.3 mm diameter. Females remain over their eggs throughout embryonic development, leaving the site only after dispersion of the nymphs begins. The post-embryonic phase contains six nymphal stages, which are characterized both morphologically and morphometrically, and lasts about 1.5 years. Secondary sexual dimorphism appears during the post-embryonic development. The adult phase lasts more than 2 years, giving a total life-span of more than 3.5 years.