Abstract: A 1:1 matched case-control study was condueted to investigate the etiology of childhood leukemia .It was found that there were three main iatrogenic risk factors: (1) Children's postnatal X-ray exposure, OR = 4.53; (2) Children took choram-phenicol,OR = 3.60; (3) Children took antipyretic/analgesic drugs, OR = 1.93. The analysis of the population attributable risk showed that 71% case of childhood leukemia can attributed to these three risk factors.The interaction among the risk factors was estimated, the result showed that there was a positive interaction be-tween the X-ray exposure and chorampphenicol on additive model.Based on the mul- tiplicative model, it showed a positive interaction between choampphenicol and an-tipyetic/nagesic drugs.