Provided herein are methods of determining a subject's level of exposure to radiation and methods of determining a subject's risk of subsequent development of radiation disease or risk of poor prognosis from radiation exposure that include determining a level of one or more miRNAs selected from the group consisting of mouse and human homologues of mouse miR-130a-3p, miR-150-5p, miR-17-3p, miR-187-3p, miR-194-5p, miR-27a-3p, miR-30a-3p, miR-30c-5p, miR-142-5p, miR-342-3p, miR-34b-3p, miR-126-3p, miR-320-3p, miR-136-5p, miR-33-5p, miR-142a-3p, miR-706, miR-375-3p, miR-29a-5p, miR-193a-3p, miR-99b-5p, miR-151-3p, miR-let-7d-3p, miR-486-5p, miR-423-5p, miR-30b-5p, miR-191-5p, miR-497a-5p, miR-32-5p, miR-214-5p, miR-326-3p, miR-1195, miR-122-5p, miR-1839-3p, miR-500-3p, miR-30e-3p, miR-322-3p, miR-709, miR-486-3p, miR-133a-3p, miR-676-3p, miR-744-5p, miR-29a-3p, miR-1839-5p, miR-30a-5p, miR-199b-5p, miR-125a-5p, miR-133b-3p, miR-24-3p, miR-21a-5p, miR-503-5p, miR-328-3p, miR-let-7g-5p, miR-362-3p, miR-199a-5p, miR-15a-3p, miR-139-5p, miR-149-5p, miR-29b-3p, miR-1a-3p, miR-23b-3p, miR-215-5p, miR-204-5p, miR-200b-5p, miR-25-3p, miR-338-3p, and miR-196b-5p, in a sample including a biological fluid from the subject.