Laboratory and field observations in 1994–2004 made it possible to ascertain the following parameters of life cycle of Valvata piscinalis (O. F. Müller, 1774). In favourable food conditions (filamentous diatoms) female maturity was attained in 42–85 days from hatching (mean 59 days) at the body whorl diameter of 3.45–4.65 mm (mean 4.10 mm) and the number of whorls 3.25–3.75 (mean 3.53). In slightly less favourable food conditions (periphyton) the maturity was attained later at a somewhat lower mean shell size. The number of cocoons and eggs produced during lifetime by snails kept in pairs was 18–113 and 387–2,862, respectively; the number of eggs per cocoon ranged from 0 to 76. Among singly kept snails only half laid cocoons (maximum 7 cocoons/6 eggs during lifetime), and the eggs failed to develop. The mean life span of snails fed mainly with periphyton was ca. 1 year (maximum 641 days); it was distinctly shorter in snails fed with filamentous diatoms (usually 5–7 months, rarely more than 11 months). In very unfavourable food conditions (small quantities of periphyton) female maturity was attained only after 1–2 years and the life span was not much longer: maximum 830 days. In natural conditions (lake Sosnowe near Sąpolno) reproduction started in the second half of April and lasted till half of July; the cocoons contained 10–37 eggs.