Scientists analysed data on almost 16,500 children in the UK who were diagnosed with the blood cancer between 1962 and 2008.
They found no evidence that children born after the 1980s whose mothers lived within a kilometre of power lines had a greater than average risk of developing the disease. A previous study focusing on leukaemia cases diagnosed between 1962 and 1995 had pointed to an increased risk for children born within 600 metres of the electric cables.
The new study strongly suggested there was no direct biological effect from power lines helping to trigger childhood leukaemia, the scientists said. They said the earlier finding could be explained by changes in the characteristics of people living near power lines, pure chance, or problems with the study design.
Kathryn Bunch, from the Childhood Cancer Research Group at Oxford University, who led the new investigation, said: "More research is needed to determine precisely why previous evidence suggested a risk prior to 1980, but parents can be reassured from the findings of this study that overhead power lines don't increase their child's risk of leukaemia."
The research was funded by the charity Children with Cancer UK.
Dr Julie Sharp, head of health information at Cancer Research UK, said: "This study is reassuring for anxious parents."