Thirty years ago, Nancy Wertheimer and Ed Leeper published the first report on the association between childhood cancer and "electrical current configuration" of houses in Denver, Colorado. In 2001 the International Agency for Research on Cancer defined 50-60 Hz magnetic fields as "possibly carcinogenic to humans" because of the "limited evidence" of carcinogenicity of residential exposure relatively to childhood leukemia. With respect to health effects other than cancer, namely neurodegenerative disorders, miscarriage, subtle differences in the timing of melatonin release, altered autonomic control of the heart, and changes in the number of natural killer cells, some open questions still remain. Several authors recommended further investigation of the possible long-term effects of magnetic fields, focussing on populations experiencing high exposure levels. In this frame a research team of ISS searched for a suitable location to implement an epidemiological study aimed at a wide range of outcomes for which a priori hypotheses could be formulated. The recently published findings of this project showed an increase of primary and secondary malignant neoplasms, ischaemic disease and haematological diseases. Future studies should thus address the most exposed sectors of the population, take into account different outcomes (all neoplasms, neurodegenerative diseases, immunological disorders, specific cardiovascular effects) and follow research protocols that enable subsequent pooled analyses. A precautionary approach may provide the frame for decision making where the available resources for environmental remediation be prioritatively allocated to worst-off situations.