Many investigators have studied the effects of Extremely Low Frequency-Magnetic Fields generated byordinary and domestic power lines, as a risk factor in acute leukaemias of children, but there are limitedinformation available regarding very high voltage overhead power lines. Children in developing countriessometimes live very close to such structures and we have registered several patients with acute leukaemiasappearing in clusters. In the present study we have analyzed 60 consecutively diagnosed patients with acuteleukaemias, and 59 matched controls in a provincial capital city in North-Western Iran. After provision ofconsent, a detailed form was filled in, and a visit to the present (or previous) residential areas of both groups wasarranged. The locations of the very high voltage power lines (123, 230, 400 kilo volts), were noted in each area,if present, and their distances from the houses under study were detected. The expected intensities of the MagneticFields (B) were calculated having the mean intensity of the electrical current and other line characteristics, bymeans ofÅırelevant equations. Fourteen patients in the case group (23.5%) were living near the high voltagepower lines in distances ≤ 500 meters. (Mean B = 0.6 microTeslas, μT). In the control group at the same distance,the figure was 2 children (3.3%) (Mean B = 0.35 μT). Statistically, the likelihood of leukaemia was increasedconsiderably in this distance (Odds ratio (OR) = 8.67, 95% Confidence Interval (CI) = 1.74- 58.4, P value=0.001). On the other hand 15 pts(25 %) in the leukaemia group were experiencing Magnetic fields above 0.45μT in comparison to 5 in the control group ( 8.5% )(OR = 3.60, 95% CI = 1.11-12.39, P = 0.01). More childrenin developing countries like Iran live close to very high voltage lines, and they experience relatively more harmfuleffects from the Magnetic Fields, in comparison with children in developed countries. Residence near very highvoltage overhead power lines, in distances ≤500 meters, and Magnetic Fields > 0.45 μT, should be considered arisk factor for the pathogenesis of acute leukaemias in children.