We sought to determine the effectiveness of early routine percutaneous coronary intervention (PCI) post-fibrinolysis for ST-elevation myocardial infarction (STEMI) in relation to baseline risk status. In this post hoc subgroup analysis of Trial of Routine Angioplasty and Stenting after Fibrinolysis to Enhance Reperfusion in Acute Myocardial Infarction (TRANSFER-AMI), we stratified 1059 STEMI patients receiving tenecteplase into low-intermediate [Global Registry of Acute Coronary Events (GRACE) risk score<155; n=889] vs. high-risk (GRACE risk score ≥155; n=170) groups, based on the GRACE risk score for in-hospital mortality. There was a significant interaction between treatment assignment and risk status for the composite endpoint of death/re-MI at 30 days (P for interaction<0.001). Compared with the standard treatment, pharmacoinvasive therapy (early routine PCI) was associated with a lower rate of death/re-MI at 30 days in the low-intermediate risk stratum (8.1 vs. 2.9%, P<0.001), but a higher rate of death/re-MI in the high-risk group (13.8 vs. 27.8%, P=0.025). We found similar heterogeneity in the treatment effects on 30-day mortality and death/re-MI at 1 year (P for interaction=0.008 and 0.001, respectively), when the GRACE risk score was analysed as a continuous variable (P for interaction<0.001) and when patients were stratified by the Thrombolysis In Myocardial Infarction (TIMI) risk score (P for interaction=0.001). We observed a strong heterogeneity in the treatment effects of a pharmacoinvasive strategy after fibrinolysis for STEMI, which is associated with improved outcomes only among patients with a low-intermediate GRACE risk score. Conversely, the early invasive strategy is associated with worse outcomes in high-risk patients. These novel findings should be considered exploratory only and require confirmation in other trials and meta-analyses. http://www.clinicaltrials.gov/ct2/show/NCT00164190 ClinicalTrials.gov number, NCT00164190.