OBJECTIVES: To study the relation between the risk of acute myocardial infarctions (AMI) and meteorological variables and the geomagnetic field, and to make a literature survey of the relation between environmental variables and the occurrence of disease. STUDY DESIGN: Register study and literature search. METHODS: Register data on AMI were analysed together with data on temperature, relative humidity, barometric pressure, the Arctic Oscillation, the earth's magnetic field, and changes in these variables. A PubMed search for studies on environmental variables and the occurrence of other diseases was done. RESULTS: There was no correlation between "static" weather variables and the number of AMIs. A temperature rise of one degree C was associated with an increase in the number of non-fatal AMIs by 1.5%. There was a strong correlation between the AO and the number of AMIs--a one unit increase in AO caused an increase in the number of surviving AMIs by 3.4%, fatal AMIs by 5.1% and the number of sudden cardiac deaths by 8.3%. There was no association between the geomagnetic field and the number of AMIs. The literature study revealed that several other disease states were related to extremes of or changes in weather situations. CONCLUSIONS: A change in weather, rather than weather extremes, was associated with an increase in the number of AMIs. The environment surrounding us is capable of causing both disease and symptoms. The triggering mechanisms are not known, though.