High voltage power lines are lines with 110kV or more volts. The first study about the topic that these high electricity power lines might have health impacts was done in 1979, after that many studies have been performed and there are some hints that living close to a high voltage power lines increases the risk of getting leucimia. In conclusion, science can neither prove or disprove this because it is unknown if low-level electromagnetic fields have an impact on human health.
Source: http://www.hps.org/hpspublications/articles/powerlines.html
