This report assesses the levels and effects of exposure to ionizing radiation. The scientific annexes provide the supporting scientific rationale for UNSCEAR’s 2019 report. Annex A focuses on evaluation of selected health effects and inference of risk due to radiation exposure described in five scenarios for risk evaluation: 1) leukemia after medical computed tomography scans during childhood; 2) leukemia after occupational radiation exposure; 3) solid cancer after occupational exposure; 4) thyroid cancer after exposure during childhood or adolescence; and 5) circulatory diseases after acute radiation exposure. Quantitative risk estimates are presented based on epidemiological studies and on the effects found among survivors of atomic bombings in Japan. Annex B focuses on the evaluation of lung cancer from exposure to radon.