STUDY OBJECTIVE: An evaluation of the effect of ambient temperature on morbidity from acute coronary syndromes (ACS) while avoiding confounding by air pollution. DESIGN: An ecological study in rural Greece. METHODS: Daily admissions to hospital because of ACS were recorded for 1 year and analysed versus daily temperature and humidity. RESULTS: For a 1 degrees C decrease in temperature there was a 1.6% (95% confidence interval 0.9-2.2%) increase in admissions. This effect was more prominent in the elderly. No difference was detected according to sex or type of ACS. CONCLUSION: It is important to implement measures against cold in coronary heart disease prevention, irrespective of air pollution.