The relationship of plasma cholesterol-reducing interventions to emotional states, such as depression and hostility, remains a topic of debate. The present study employed a randomised, controlled design, and was conducted at a clinical research center to test the effect of dietary cholesterol-lowering on psychological symptoms. Ten women and eight men were randomly assigned to one of two counterbalanced diet cycles (low-fat versus high-fat diet; isocaloric; 6 weeks each; separated by a washout period). Analyses for repeated measures revealed that the low-fat diet significantly reduced total, LDL and HDL cholesterol, when compared with baseline and the high-fat diet. As expected, weight remained unchanged. Ratings of depression, hostility and global severity of psychological symptoms as measured by the SCL-90-R also improved significantly on the low-fat, high-complex carbohydrate diet when compared with baseline. These results suggest that plasma cholesterol-lowering in the context of a low-fat, high-complex carbohydrate diet may have a beneficial effect on psychological symptoms.