This paper identifies factors affecting the distribution of farm income among dairy producers over time. Using data from participants in Cornell's Dairy Farm Record Program, we decompose differences of farm income distributions into those due to: differences in means of observable farm characteristics, differential marginal effects of characteristics and unobserved random error. The distribution of farm income is affected by factors reflecting the operators' experience and investment in human capital and indicators of management efficiency and level of capital investment. The marked changes in marginal contributions of these factors explain most of the total change in the distribution of income.