BACKGROUND: Meteorological factors like cold temperatures and heavy snowfalls have been reported to increase myocardial infarction (MI) incidence, but there are inconsistencies in results as well as in methodology in previous studies. The objective of this study was to examine the impact of meteorological factors on incidence of MI in a population-based study in Tromso, Norway (69 degrees 39'N). METHODS: A total of 32110 participants from the Tromso Study enrolled between 1974 and 2001 were followed throughout 2004. Each incident case of MI was validated by the review of medical records and death certificates. Meteorological data from the Tromso Weather Station were collected from the Norwegian Meteorological Institute database. Poisson regression models were applied to analyse the impact of meteorological factors on MI incidence. All analyses were stratified by sex and age. RESULTS: A total of 1882 first-ever MIs were registered. The main finding was an increase in MI incidence among persons older than 65 years with decreasing temperatures (pEuro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin)0.016) and increasing snowfall (pEuro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin)0.030). When comparing the lower and upper limits of the temperature distribution (-10 degrees C with 20 degrees C), the MI risk increased by 47% (RREuro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin)1.47, 95% CI 1.09 to 2.13). Comparing limits of the snowfall distribution (10 with 0 mm), the MI risk increased by 44% (RREuro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin)1.44, 95% CI 1.07 to 1.94). CONCLUSIONS: In this subarctic population, MI incidence was little affected by the weather, probably due to behavioural protection. However, cold weather and heavy snowfall may be associated with increased risk of MI among older people.