Abstract: The technical efficiency and viability of organic dairy sheep farming systems were investigated in Castilla-La Mancha, a Spanish region with a tradition of sheep rearing. The thirty one farms sampled, had an average of 359ha, 508 sheep and 1.9 work units (WU); the reproductive rate was 1.5 lambs per ewe and year and the human productivity reached 303 sheep/WU. There was however a high degree of variation among farms. Although the average level of technical efficiency was 66%, 74% of farms sampled operated at medium or low rates of technical efficiency. Differences in technical efficiency were largely due to the consumption of feeding supplements and productivity. A total of 45% of the farms was classified as non-viable. It was concluded that strategies for improving competitiveness and the use of resources are specific to each level of efficiency. The most efficient farms must increase their size; moderately efficient farms need to focus their efforts on improving the management of resources to enhance results. Improving competitiveness of the less efficient farms requires an increase of productivity; a better balance between the use of feeding supplements and the sheep productive capacity. [Copyright &y& Elsevier]