Leptin is a protein hormone produced by adipocytes that reflects the body fat content, i.e., its serum concentration in healthy individuals positively correlates with the body mass index and body fat content. Serum leptin levels are lower in both patients with anorexia nervosa and protein-caloric malnutrition caused by chronic non-malignant illnesses. The aim of the present study was to compare serum leptin levels and selected, routinely used nutritional parameters in women with anorexia nervosa (n = 17), severely malnourished patients with short bowel syndrome (n = 13), and control non-obese healthy women (n = 17) to clarify the relation between selected nutritional parameters and serum leptin levels. We found that serum leptin levels in the anorexia nervosa and short bowel syndrome groups were significantly lower than those in the control group (in ng/mL: 3.63 +/- 1.64 and 2.59 +/- 1.17 versus 12.06 +/- 7.59, respectively). Protein malnutrition expressed by decrease in serum concentrations of total protein, albumin, and prealbumin was more pronounced in the short bowel syndrome group. Triceps skin fold, arm muscle circumference, and body mass index were significantly lower in the patient group than in the control group and did not significantly differ between the short bowel syndrome and anorexia nervosa groups. No significant difference in serum leptin concentration between the short bowel syndrome and anorexia nervosa groups was found. Serum leptin levels correlated positively with body mass index and triceps skin fold in the control and anorexia nervosa groups but not in the short bowel syndrome group. We conclude that serum leptin levels in patients with anorexia nervosa and short bowel syndrome are significantly lower than in healthy individuals and have no statistically significant relation to serum total protein, abumin, and prealbumin.