The simultaneously hermaphroditic land snail Arianta arbustorum (L.) (Pulmonata: Helicidae) was long believed to be self-incompatible. In the present study, however, uniparental reproduction was observed under laboratory conditions. Snails from two natural populations and from laboratory culture reared in isolation from the subadult stage produced fertile eggs. Over a period of three years after maturation, 38.5% of the unmated snails produced fertile eggs, mostly in the second and third years instead of the first year. Egg production and hatching success (the proportion of eggs that hatched) were lower in unmated snails than in mated snails. The number of hatchlings produced by unmated snails was 1–2% of that produced by mated snails. Hatchlings from unmated snails survived as well as those from mated snails under laboratory conditions. The result indicate that A. arbustorum can self-fertilize but with a great fitness reduction.