The present study aims at quantifying the variation of organ doses due to the variation of entrance doses and the varying anatomical position of single organs among different patients and at emphasising the limitations of dose assessments using literature values only, without performing any measurements. Entrance doses were measured for 93 patients undergoing intravenous pyelography with the same X ray equipment. It was found that the entrance doses varied by up to a factor of 4.7, even for patients with the same abdominal diameter (AP). As an example of the deviation of an individual patient's anatomy from that of a 'standard' patient, the variation of the position of the uterus was studied using computed tomography data from 103 patients. For the different uterus positions found, uterus doses for a pelvis AP examination were estimated for constant entrance dose using a depth-dose curve in water. Among patients with a diameter of approximately 19 cm the doses varied by a factor of 2.7.