The majority of obese persons have hyperinsulinemia and disturbances in the secretion of melatonin, catecholamines and pituitary, thyroid, adrenal and gonadal hormones. These hormones play an important role in the regulation of collagen metabolism either by acting directly or by influencing IGF-I production. This study aimed at ascertaining whether, and to what degree, the changes in the concentration of hormones listed above as well as in the concentration of sex hormone-binding globulin (SHBG) and insulin-like growth factor-I (IGF-I) affect the metabolism of collagen as evaluated indirectly from the measurement of propeptides of type I (PICP) and type III procollagen (PIIINP) in blood serum and hydroxyproline in urine. The study compared 30 women with extreme obesity before and three to five years after jejunoileostomy with 20 healthy women of reproductive age. All non-operated obese women showed significantly increased concentration of serum insulin, IGF-I, melatonin, norepinephrine, free triiodothyronine, estradiol, total and free testosterone, PICP, PIIINP and urinary excretion of hydroxyproline, while the levels of epinephrine, progesterone and SHBG were significantly decreased. Changes in the level of the examined markers of collagen metabolism correlated positively with the concentration of insulin, IGF-I and sex hormones, while the correlation with epinephrine, cortisol and thyroid hormones was negative. All women who were treated previously by jejunoileostomy showed a decreased of body mass to regular values, normalization of hormonal disturbances and normal collagen metabolism. The obtained results show that the increased collagen metabolism observed in extremely obese women is caused indirectly by altered endocrine activity.