Mean platelets volume (MPV) has been shown to correlate with impaired reperfusion and increased mortality in patients with ST-elevation myocardial infarction (STEMI) treated with primary precutaneous coronary intervention (PCI). We aimed to study whether the same association exists in STEMI patients treated with thrombolysis. Included in the study were STEMI patients receiving thrombolysis. Thrombolysis failure was defined as a need for rescue precutaneous coronary intervention (PCI), in-hospital mortality, unplanned PCI during hospitalization or complete occlusion of the culprit coronary artery in a follow-up angiography. MPV levels were compared between patients with failed or successful thrombolysis. Of the 122 patients, 30 had failed thrombolysis while the other 92 fulfilled the criteria for successful treatment. There were no significant differences in demographic or clinical baseline characteristics of the two groups. Mean MPV was significantly higher in patients with failed thrombolysis compared to patients with successful treatment (9.2 +/- 1.1fl and 8.7 +/- 1.0fl respectively, p = 0.019 in multivariate analysis). The prevalence of thrombolysis failure was significantly higher in patients with MPV > 8.6 fl compared to those with MPV </= 8.6 fl (31.8% and 16% respectively, p = 0.048 in multivariate analysis). It appears that higher MPV correlates with thrombolysis failure in patients presenting with STEMI. MPV may be used as an adjunctive readily available factor for assessing thrombolysis outcome upon admission.