Background: Diagnostic radiology by the use of ionizing radiation plays a main contribution in the collective dose of human population. Knowing the radiation dose received by patients during a radiological examination is essential to prevent the excess health risk of exposure. Objectives: The aim of this study was to estimate the collective dose and calculate the cancer risk probability due to common radiological procedures in four radiology imaging centers of Iran. Patients and Methods: Four hundred seventy patients who underwent different radiological examinations including the skull, chest, abdomen, pelvis, lumbar, cervical and thoracic regions in four radiology centers of Hamadan, Iran were studied. The patients' entrance surface dose (ESD) was measured, and eventually, the effective dose (ED) was calculated. These parameters were compared with the reported values and international standard levels. Finally, the risk of cancer was determined by two different methods proposed in international commission on radiological protection (ICRP) 103.