As farms become larger and more specialized, questions of the relationships between costs and income as affected by size become more important. This report on cost-size relations on irrigated cotton farms in the San Joaquin Valley, Calif., shows that the smaller farms, within the range of size illustrated, can pay current charges for irrigation water and remain "in the black." However, their profits disappear more readily than those on larger farms as costs of irrigation water increase. On the farms illustrated, most of the economies of scale and size are achieved by the 320-acre farm. Costs per dollar of output increase rapidly for successively smaller farms, but decrease slowly for successively larger ones.