The mineral content of bone was measured in 134 male patients who underwent ureterosigmoidostomy within the past 18 years. Moreover, the principal humoral indices of bone metabolism, together with hematic pH and alkaline reserve (BE) values were evaluated. This study showed that after approximately 6 years from a ureterosigmoidostomy there was significant bone demineralization. These data, supported by a parallel increase of serum osteocalcin, show that ureterosigmoidostomy represents a risk factor for osteoporosis especially in those patients who already have below normal values of bone mineral density prior to surgery.