The Diet Habit Survey was designed to identify eating habits and measure dietary changes made over time by 442 adults in the Family Heart Study, a coronary heart disease prevention project. Reliability was determined by test-retest analysis. Validity was assessed by comparison with 24-hour dietary recalls and by comparing changes in diet with changes in plasma cholesterol levels. At baseline, 89% of the subjects were classified as eating the current American diet (37% fat), 10% reported eating Diet 1 (30% fat), and 1% reported eating Diet 2 (25% fat). After 5 years of dietary intervention, the population's eating habits had shifted; 48% reported eating the current American diet, 37% reported Diet 1, 14% reported Diet 2, and 1% reported Diet 3 (20% fat). Significant plasma cholesterol lowering was associated with changes in Diet Habit Survey scores reflecting lower cholesterol and saturated fat and higher complex carbohydrate intakes. This questionnaire is an inexpensive, reliable, and valid instrument for rapid assessment of eating habits and diet composition and, thus, is an important new tool for dietetics researchers and practitioners.