Spermatogenesis in amphibians occurs inside spermatogenic cysts formed by Sertoli cells (SCs). SCs do not constitute a permanent population and their number increases during spermatogenic cycle and ontogeny. The number of SCs per cyst is strongly correlated with the number of germ cells in the same cyst and with the cyst volume. The number of germ and Sertoli cells and cyst volumes are species-specific and increase along with age. The mean number of primary spermatocytes per one Sertoli cell (efficiency) was the same, irrespective of age and species. Late spermatids are not attached to the Sertoli cells and do not form bundles as in other amphibians. The number of primary spermatocytes inside a cyst was the yield of several mitotic cycles of a single primary spermatogonium (stem cell) and its descendants, i.e., secondary spermatogonia. In adult Bombina bombina, the majority of cysts contained germ cells after 6–8 cycles, in juveniles after 4–6 cycles, and in adult Bombina variegata after 5–7 cycles. The mean numbers of SCs per cyst were 27.4 ± 9.9 in adult B. bombina, 6.42 ± 2.32 in adult B. variegata, and 7.1 ± 2.33 in juvenile B. bombina. The number of primary spermatocytes per one SC (SC efficiency) in B. bombina in adults was 6.5 ± 2.2, in juveniles 9.0 ± 4.2, and in adult B. variegata 7.40 ± 2.96. Spermatogenesis in Bombinatoridae is exceptional owing to the lack of intimate contact between SCs and germ cells.