In 1982, we proposed a large-scale randomized prospective trial to test the hypothesis that decreasing dietary fat intake from 38% to 20% of total calories would increase the disease-free interval and/or five-year survival rate for postmenopausal breast cancer patients. We now review new evidence from epidemiological studies, laboratory animal model studies, and preliminary feasibility trials that has accumulated over the past decade, in support of such a trial, and suggest that a more appropriate dietary goal is a reduction in fat intake to 15% of total calories.