OBJECTIVES: The aim of this study was to evaluate the consequences, measured as mortality and in-hospital stroke, of the use of thrombolytic therapy among patients with acute myocardial infarction (AMI), who do not fulfill accepted criteria or who have contraindications to thrombolytic therapy (i.e., overutilization) and among patients who are withheld thrombolytic treatment despite fulfilling indications and having no contraindications (i.e., underutilization). BACKGROUND: The implementation of treatment with thrombolysis in clinical practice is not in accordance with the accepted criteria from randomized studies. The consequence has been over- and underutilization of thrombolytic therapy among patients with AMI in clinical practice. The outcome of overutilization of thrombolytic therapy has not been described previously. METHODS: We examined 6,676 consecutive patients admitted to the hospital with an AMI and recorded characteristics, in-hospital complications and long-term mortality. RESULTS: Overall, 41% of the patients received thrombolytic therapy. Thrombolytic therapy was underutilized in 14.3% and overutilized in 12.9% of the patients. The use of thrombolytic therapy was associated with reduced mortality in every subgroup examined, including patients without an accepted indication, with an accepted indication and in patients with prior stroke. The risk ratio of in-hospital stroke was not increased in connection with thrombolytic therapy, not even in patients with prior stroke (relative risk = 0.237, 95% confidence interval: 0.031 to 1.810, p = 0.17). CONCLUSIONS: With the large benefit known to be associated with thrombolytic therapy and the favorable result of thrombolytic therapy in patients with contraindications observed in this study, we conclude that a formal evaluation of thrombolytic therapy in wider patient categories is warranted.