Life cycle of Discus ruderatus (Fér.) was studied in the laboratory, with occasional field observations. No courtship or copulation could be observed; uniparental reproduction is very rare. In the laboratory the eggs are laid in all months, with maximum in June/July and December/January, in the field the youngest age class appears in May. The eggs are laid on rotting timber; they are calcified, nearly sphaerical, ca. 1.5 mm in major diameter; the number of eggs per batch is 1–6 (mostly 3–4), with a total of 6–15 eggs in 2–5 batches per lifetime. The incubation period is 17–34 days, hatching is nearly synchronous; the hatching success is ca. 54%. The hatchlings have shells of 1.5–2.5 whorls; they consume their egg envelopes immediately after hatching. The egg cannibalism is prolonged into adult stage. The overall mean growth rate is 1 whorl per ca. 179 days (54 days per whorl till maturity, 487 days per whorl in mature snails). The snails reach maturity at slightly over 4 whorls (mature gametes present in the gonad), the mean life span is 580 days, the reproductive life constituting ca. 35% total life span. Life cycle parameters of three members of Discus are discussed comparatively.