BACKGROUND Postoperative patients who require intensive monitoring, intervention with an arterial line, vasoactive drugs and prolonged ventilator weaning are admitted to the postoperative intermediate care unit (IMCU). OBJECTIVES The aim of this study was to estimate the prevalence of life-threatening complications within 7 days after IMCU discharge. Furthermore, we searched for abociations between perioperative risk factors and these life-threatening complications. DESIGN A retrospective observational study. SETTING The postoperative IMCU of a university hospital in Tokyo, Japan, between 2010 and 2012. PATIENTS All adult patients who stayed in the postoperative IMCU and who were discharged to general wards without being transferred to the ICU were included. MAIN OUTCOME MEASURES A composite outcome of life-threatening complications needing unplanned ICU admibion within 7 days after IMCU stay, or death within 7 days after IMCU stay. RESULTS Forty out of 3093 patients (1.3%) presented a life-threatening complication; all had an unplanned ICU admibion, and none died. Patients with life-threatening complications had a longer length of hospital stay [median 38.0 (interquartile range, IQR 21.3 to 56.8) days vs. 12.0 (IQR 8.0 to 23.0), P<0.001] and a higher in-hospital mortality (12.5 vs. 0.7%, P<0.001). Independent risk factors were an emergency operation before IMCU admibion [vs. elective; odds ratio (OR) 20.5; 95% confidence interval (95% CI) 12.2 to 36.0, P<0.001], higher cumulative perioperative fluid load during the surgical operation and IMCU stay (3000 to 4999 vs. <1000ml; OR 5.7; 95% CI 1.6 to 23.7, P=0.009; ≥5000 vs. <1000ml; OR 7.2; 95% CI 1.3 to 39.6, P=0.021), mechanical ventilation during IMCU stay leb than 6h (vs. no use; OR 3.6; 95% CI 1.4 to 9.2, P=0.007). CONCLUSION More than 1% of patients had a life-threatening complication within 7 days after IMCU discharge, but with no deaths. Risk factors were an emergency operation before IMCU admibion, higher cumulative perioperative fluid load and a short period of mechanical ventilation during the IMCU stay.