Six hundred years before Christ, Hippocrates said that physicians on exercising their medical duties, should benefit but not harm their patients. Seventy years ago increased medical radiation caused radiologists in the US an excess risk of leukemia, lymphoma and multiple myeloma. Now medical radiation is rather safe for the physician but the question remains if proper prophylactic measures are being taken to make it safe for the subjects examined. Roughly, first trimester of pregnancy radiography has a much greater fatal cancer risk than that of exposures taken later in pregnancy. It is suggested that women should be administered the minimum activity consistent with achieving the desired clinical information, whether or not they are known to be pregnant. The best available risk estimates suggest that pediatric CT diagnostic procedures will induce significantly increased lifetime radiation risk in children. Professor Roger Clarke wrote that there may be a need to reduce or prevent doses of medical radiation up to 3 mSv if there is no benefit to the individual. 30 mSv is described as "a dose which should not be exceeded" and can be approached only if there is a benefit to individuals and the dose is difficult to reduce or prevent. In WHO Category III a) Static brain imaging with technetium-99m pertechnetate, b) Gated cardiac imaging c) Bone imaging with technetium-99m MDP, c) Quantitative haemodynamics with technetium-99m pertechnetate, d) myocardial imaging with thallous-201 chloride and e) abscess imaging with gallium-67 citrate, induce an effective dose equivalent of 5-9 mSv. A CT scan commonly gives 25 mSv to the subject examined. BEIR VI indicated that a 10 mSv single population dose is associated with a lifetime attributable risk for developing a solid cancer or leukemia in 1:1000. Multiple CT examinations have administered to some patients with renal colic a dose of 19.5-153.7 mSv. One may suggest that there should be "justification" and informed written patients' consent for nuclear medicine examinations administering to the patient doses greater than 5 mSv, especially doses around or above 30 mSv / year.