Irrigation represents an important tool to increase forage yield and animal performance in Sardinian lowlands but the intensification is strongly dependent on the economic advantages that it can offer to the dairy sheep farmers. Four system models differing in agronomic inputs and feeding regimes were studied with the aim of evaluating the output/input balance of irrigated dairy sheep farming systems during 1994-1996. They consisted of two groups fed on pasture and differing in lambing season, group A lambed in autumn whereas group W at the end of winter, the stocking rate was 20 ewes ha-1. The other two system models with a stocking rate of 33 ewes ha-1 differed in feeding regimes: group CD (zero grazing) was fed with a complete diet containing hay, silage and concentrates, group CDP in addition to the complete diet, grazed Italian ryegrass throughout the lactation period, for 3-5 h day-1. The forages were lucerne and white clover (only in A and W) and Italian ryegrass, replaced in summer by sorghum and maize (only in CD and CDP). The percentage ploughed each year was 47 per cent in both A and W whereas in CD and CDP systems was 81 per cent. Milk production per ha was on average 4.78 in A, 5.26 in W, 6.04 in CD and 6.50 t ha-1 in CDP and weaned lambs production in tons per hectare were on average 0.29, 0.31 in A and W, 0.45, 0.46 in CD and CDP. However the economic return is higher for grazing than housed systems that have higher production cost. On the basis of these results intensive production systems can increase stocking rate and milk production per ha; in particular it is possible to plan the lambings and delay part of milk production in summer.