BACKGROUND: Various efforts to reduce patient delay in acute coronary syndrome (ACS) have had limited success. One reason might be a misinterpretation of the symptoms of ACS. The aim of this study was therefore to explore the characteristics and severity of symptoms among patients with an ACS in overall terms and in relation to the type of ACS, sex, age, and diabetes. METHODS: A total of 1939 patients at 11 hospitals in Sweden answered a questionnaire containing questions relating to the localization and intensity of symptoms, the presence of associated symptoms, the characteristics and experience of pain/symptoms, and the type of symptom onset. RESULTS: Patients with ST elevation differed from those without by more frequently having associated symptoms. They had higher pain/discomfort intensity and more frequently had pain with abrupt onset reaching maximum intensity within minutes. However, this type of symptom onset was only seen in less than half the patients with ST elevation and only 1 in 5 fulfilled all the criteria usually associated with a severe heart attack. Women differed from men in a few respects. They more frequently reported pain/discomfort in the neck or jaw and back, vomiting, and scored their pain/discomfort slightly higher than men. Differences between age groups were minor and there was no difference between patients with and without diabetes. CONCLUSIONS: The most striking finding was the low proportion of patients with the type of symptoms that are commonly associated with ACS. This is important for the planning of educational campaigns/programs to reduce patient delay.