Background: Treatment of ST-elevation acute myocardial infarction has primary percutaneous coronary intervention as the preferred method of reperfusion. This study aimed to evaluate in-hospital outcomes of patients with ST-elevation acute myocardial infarction according to the total ischemic time until performing primary percutaneous coronary intervention. Methods: Single-center registry of patients admitted with ST-elevation acute myocardial infarction undergoing primary percutaneous coronary intervention between March/2012 and February/2014, followed from admission to hospital discharge, and compared according to the total ischemic time (Group 1: symptom onset-to-balloon time < 6 hours; Group 2: symptom onset-to-balloon time ≥ 6 and < 12 hours). Results: Two hundred seventy nine patients underwent primary percutaneous coronary intervention, 118 in Group 1 (42.3%) and 161 in Group 2 (57.7%). Group 2 was older, had higher prevalence of hypertension, fewer smokers, more patients in Killip-Kimball class ≥ 2 and lower primary percutaneous coronary intervention success rate. The incidences of death or non-fatal infarction (11.0% vs. 18.6%; p = 0.08), death (8.5% vs. 16.8%; p = 0.04) and acute renal failure (7.6% vs. 19.9%; p < 0.01) were greater in Group 2. Conclusions: Patients with ST-elevation acute myocardial infarction undergoing primary percutaneous coronary intervention with symptom onset-toballoon time ≥ 6 hours presented higher clinical complexity and worse in-hospital outcomes when compared to patients treated earlier. Joint actions in different critical areas of patient care are essential to increase treatment efficacy and reduce adverse outcomes.