This report examines the maintenance of a low-fat diet 1 year on average after the completion of intervention sessions among participants in the Women's Health Trial (WHT). The WHT was a randomized controlled trial of the feasibility of adoption of a low-fat diet among women of moderate or increased risk of breast cancer, conduced in Seattle, Houston, and Cincinnati in 1985-1988. The women randomized to the low-fat diet attended an intensive dietary intervention program for 5-37 months. Intervention women were highly successful in reducing their dietary fat intake from 40.0% of energy intake at baseline to 26.3% by the end of the trial, based on a food frequency questionnaire (or an estimated 24% adjusted for the inaccuracies of a food frequency questionnaire versus a 4-day diet record). During 1989, 1 year on average after the WHT ended, 448 intervention women and 457 control women (87% of eligibles) completed a follow-up survey to determine the degree of maintenance of the diet. The intervention women maintained the low-fat diet with an increase of only 1.4 percentage points of energy from fat, despite the fact that they had attended no further intervention sessions and had made no commitment to maintain the diet beyond the end of the WHT. Furthermore, the degree of maintenance of the low-fat diet was not dependent on the length of time in the intervention, which suggests that intervention led to a sustained change in eating habits after as little as 5-9 months (8-13 classes).(ABSTRACT TRUNCATED AT 250 WORDS)