Damage to the microcirculation caused by high-dose ionizing radiation is well known but data concerning low-dose exposure are scant and contrasting. We employed capillary microscopy to study dermal microcirculation damage resulting from occupational exposure to ionizing radiation doses lower than 5 rem/year (maximum permissible dose in Italy). We studied 145 physicians (60.7% radiologists, 33.8% orthopedic specialists, 5.5% cardiologists) occupationally exposed to ionizing radiation and a control group of 106 subjects in comparable but different occupations not exposed to ionizing radiation or to other skin hazards. All subjects were administered a clinical protocol and underwent capillary microscopy of the fingernail-fold. Capillary microscopy alterations were classified as absent, mild, moderate, marked and severe. Our data confirm that occupational exposure to low-dose ionizing radiation can lead to morphological and functional alterations of the dermal microcirculation, which can be identified early by capillary microscopy.