Hypercholesterolaemia is a common finding in patients with anorexia nervosa (AN). To investigate the type, frequency and pathophysiological mechanisms of changes in lipoprotein metabolism in AN we performed a cross-sectional study in fifty-eight female patients (mean age 24·2 years, BMI 15·3 (SD 1·5) kg/m2) and fifty-eight healthy age-matched controls (CO; BMI 22·2 (SD 1·7) kg/m2). Total cholesterol and LDL-cholesterol were higher in AN (5·5 (SD 1·3) v. 5·0 (SD 0·8) mmol/l, P=0·023; 3·6 (SD 1·1) v. 3·2 (SD 0·7) mmol/l, P=0·025 respectively). LDL particles were significantly more enriched in cholesterol and triacylglycerol in AN. In multiple regression analysis with LDL-cholesterol as the dependent and BMI, total body fat ( %), lathosterol:cholesterol ratio (endogenous cholesterol synthesis), 7α-hydroxy-4-cholesten-3-one (bile acid synthesis), non-esterified glycerol, free triiodothyronine and free thyroxine as independent variables, BMI was the only significant predictor in CO (R2 0·36, overall P=0·001). In AN the variability of LDL-cholesterol was significantly predicted by total body fat, free thyroxine, BMI, free triiodothyronine and non-esterified glycerol (R2 0·55, overall P<0·001). Subgroup analysis between restricting (AN-R) and binge-eating–purging patients (AN-B) indicated that in AN-R changes in lipoproteins, BMI and total body fat were more pronounced. AN-R patients had lower bile acid synthesis than AN-B (P=0·02). We conclude that elevated cholesterol concentrations in AN are generally due to an increase in LDL-cholesterol, which is mostly determined by the severe loss of body fat and the resulting changes in thyroid hormones, increased lipolysis and decreased endogenous cholesterol synthesis with resulting decrease in LDL removal. The clinical subtype of AN plays a major role in the mechanisms leading to hypercholesterolaemia.