A case-only study was conducted in 123 patients with sporadic acute leukemia (AL). The locations of electric transformers and power lines were noted in each area, and their distances from the houses of the study patients were measured. The intensities of magnetic fields (B) were measured in 66 cases. Unconditional logistic regression analysis was performed adjusting for age, gender, parental education and occupation, indoor and outdoor pesticides use, presence of television sets, refrigerators and microwave ovens in children's rooms and the presence of chemical factories or telecommunication transmitters within 500 m of the houses. The results of the gene-environment analyses revealed that an interaction existed between the XRCC1 Ex9 + 16 A allele and the presence of electric transformers and power lines within 100 m (Mean B = 0.14 μTeslas, μT) of the houses (interaction odds ratio, COR = 4.31, 95%CI: 1.54-12.08). The COR for the interaction of XRCC1 Ex9 + 16A and the presence of these installations within 50 m (Mean B = 0.18 μT) of the houses was 4.39 (95%CI: 1.42-13.54). Our results suggest a possible association between electric transformers and power lines and the XRCC1 Ex9 + 16A allele in patients with childhood AL.