The penetrating properties of both primary and leakage radiation was determined for a 10 MV isocentric X-ray linear accelerator. The tenth-value layer and beam profiles of the primary beam was measured at different field sizes through a 30-in. concrete wall. Transmission measurements of X-rays emitted at angles of 45, 90, 135 and 180 degrees were also obtained. This approach allowed a direct comparison of the primary beam tenth-value data with published values, thereby providing a check on the adequacy of the experimental method employed. Leakage radiation through lead and tungsten shielding around the X-ray-producing target was found to be significantly less penetrating than the primary beam.