We evaluated whether primary percutaneous coronary intervention (pPCI) during off-hours is related to an increased incidence of contrast-induced nephropathy (CIN). We retrospectively analyzed the incidence of CIN mortality among 2552 patients with consecutive ST-segment elevation myocardial infarction treated with pPCI during regular hours (weekdays 8:00 AM to 5:00 PM) and off-hours (weekdays 5:01 PM to 7:59 AM, weekends and holidays). Patients in the off-hour group were more frequently admitted with acute heart failure symptoms (16.4% vs 7.8%, P < .001) and more contrast was injected during the procedure (235.2 ± 82.3 vs 248.9 ± 87.1 mL, P = .002). The frequency of CIN between on-hour and off-hour groups was similar (7.1% vs 6.2%, P = .453), but there was a trend toward higher in-hospital mortality when pPCI was performed during off-hours (1.9% vs 0.7%, P = .081). Off-hour pPCI was not associated with an increased risk of CIN (odds ratio: 1.051, P = .833). The incidence of CIN did not increase during off-hours, and off-hour pPCI is not a risk factor for CIN, despite an apparent increase in contrast media use during off-hour pPCI.