Fixed effects production functions and stochastic production frontiers are estimated and used to decompose dairy farm output growth into technological progress, technical efficiency, and increased input use or the size effect. Unbalanced panel data for ninety‐six Vermont dairy farmers for the 1971–84 period are utilized. The results show a 2.5% average annual increase in milk output. About 56% of this growth is attributed to the size effect and the remaining 44% to productivity growth. Technological progress contributed about 94% to total productivity growth, while improvements in technical efficiency accounted for only 6%.