The present work was designed to study parameters of calcium and vitamin D metabolism in the patients presenting with morbid obesity (MO) including those who had undergone biliopancreatic diversion bypass (BPD). The patients were allocated to three groups. Group 1 was comprised of the patients with BMI in excess of 40 kg/sq.m. (n=22), group 2 included the patients after BPD (n=23), and group 3 (control) consisted of the healthy volunteers having normal body weight in the absence of signs of obesity (n=22). The three groups were significantly different in terms of consumption of vitamin D (p<0.001). Four 4 (18%) patients with morbid obesity and 12 (52%) patients in group 2 had elevated parathyroid hormone (PTH) levels that remained normal in all the subjects of group 3. The comparison of the incidence of secondary hyperparathyroidism (SHPT) in the patients of groups 1 and 2 confirmed its higher occurrence among the operated patients (p=0.029). In other words, the patients with MO significantly more frequently experience deficiency of vitamin D than the subjects of the control group (p=0.007). Examination of the patients who had undergone biliopancreatic diversion bypass demonstrated a higher incidence of SHPT developing in the late postoperative period.