Effects of season, nutritional environment and lambing management were studied on the numbers and weights of lambs produced in fine-wool sheep in southwestern New Mexico over a 2-yr period. One group of ewes was maintained and lambed on arid range (range-range). A second group was maintained on range except during lambing and early lactation (range-pasture). The third group was maintained on irrigated pasture (pasture-pasture). Groups 2 and 3 were lambed together on irrigated pasture or in drylot, depending on the season, and maintained as one group on pasture until the lambs averaged 60 d of age. At about 60 d of age, all lambs were weaned and fed in the drylot as one group. Fall lamb production was much lower (P<0.001) than at other seasons of the year. Changing the breeding time for the fall lambing from April to mid May greatly improved lamb production. The primary problems with fall lambing appeared to be a lower percentage of ewes showing estrus and a lower twinning rate. Lamb production based on birth and survival rate and weaning weights of ewes lambing on range was markedly lower to lamb production of range-managed ewes lambing in drylot or on pasture (P<0.001). The difference was primarily due to low lamb survival on the range. The causes of loss appear to be predation, deficient mothering ability and exposure. Lambing season had no real effect on wool production, but pasture-managed ewes produced 0.4 kg more grease wool than ewes kept continuously on the range (P<0.05). Lamb production can be improved by lambing ewes in drylot or on pasture, by avoiding lambing during coldest months, and by providing shelter from cold and wind the first 3 d of life.