Purpose: Radiation-induced chromosomal damage and apoptosis were compared in human lymphocytes. Materials and Methods: Peripheral lymphocytes from 10 normal volunteers (6 males, 4 females, age range 23∼41 years) were irradiated by gamma rays from a cell irradiator. Doses of irradiation were 0 (control), 0.18, 2, 5, 10, 20 and 25 Gy. Irradiated lymphocytes were examined by metaphase analysis for chromosomal aberrations and by flow cytometry for apoptosis. Results of both studies were compared according to dose. Results: Number of dicentric and ring chromosomes (D+R) was 0.5±0.53 at baseline, which was significantly increased after radiation according to the dose. The fraction of cells showing annexin V-fluore-scein isothiocyanate uptake was 0.55±0.39%, which increased to 3.58±1.85% by 2 Gy irradiation, and then decreased. The fraction of cells showing propidium iodide (PI) uptake was 0.52±0.12%, which significantly increased according to dose (upto 15.64±5.99% by 20 Gy irradiation). D+R and PI uptake were well correlated (r=0.84, p<0.001). Conclusion: Radiation-induced chromosomal aberration was correlated to nuclear uptake of PI, a marker of late apoptosis.