Background: There is public concern about the potential health effects of exposure to extremely low frequency electromagnetic fields (ELF-EMF) of high-voltage power lines (HVPLs). Some residents living near HVPLs believe ELF-EMF might cause non-specific health complaints. Objectives: The present study is the first to prospectively investigate whether self-reported health complaints and causal beliefs increase after the construction of a new power line. Methods: We used a quasi-experimental design with two pretests before and two posttests after a new HVPL was put into operation. Residents living near (0-300. m, n=229; 300-500. m, n=489) and farther away (500-2000. m, n=536) participated in the study. Linear mixed models were fitted to test whether symptom reports and beliefs that power lines caused health complaints increased more in residents living close to the new line compared to residents living farther away. Results: A significantly (. p<.05) larger increase from baseline in symptom reports and causal beliefs was found in residents living within 300. m from the new power line when compared to residents living farther away. While symptom reports did not differ at baseline, the belief that a power line could cause these symptoms was at baseline already stronger for residents living close compared to residents living farther away. Conclusions: We found a negative impact of a new HVPL on health perceptions of nearby residents, even before the line was put into operation.