Interactions between drought stress and inbreeding depression were studied in Lychnis flos-cuculi. Four inbreeding levels (F = 0, 0.25, 0.50 and 0.75), and three watering treatments were used. Performance was scored for germination rate and proportion, survival, plant size, proportion of plants flowering, flowering date, stem height, number of flowers, flower size, anther weight, fruiting proportion and number of capsules. Multiplicative fitness values were estimated from these traits. Inbreeding affected most of the traits studied, and a severe inbreeding depression was found for the combined fitness estimates. The higher inbreeding depression found here relative to the same family groups in a former experiment may reflect greater dominance and suppression in the present experiment at higher density. Drought stress exacerbated the inbreeding depression observed for survival, whereas no interaction between inbreeding and stress was found for the fecundity variables or for the combined fitness estimates. The generality and possible biological mechanisms behind inbreeding depression x environment interactions are discussed.