Introduction: The post-anaesthetic phase is most often uncomplicated, but patients may experience inadequate emergence (IE) characterized by unrest, restlessness, aggressiveness or in contrast sedation or lack of initiative. This may increase length of stay (LOS) and post-operative complications. The aim of this study was to investigate frequency, risk factors and consequences of IE. Methods: We conducted an observational cohort study including 1000 orthopaedic and abdominal surgical patients, screened with the Nursing Delirium Screening Scale (Nu-DESC) before induction of anaesthesia, at arrival at the post-operative care unit, and just before discharge from PACU. IE was defined as a Nu-DESC score ≥2 after surgery. Predictors included surgical procedure, type and duration of anaesthesia, age, ASA-score, sex and post-operative pain. Data were analysed during adjusted logistic regression and Wilcoxon rank sum test, the primary outcome being LOS. Results: IE occurred in 103 of 1000 patients (10.3%, 95% CI 8.6-12.3%). LOS was median 2 vs 1 day in patients with and without IE, mean difference was 1.3 (SD 6.2) days (P = 0.036). Thirty-day mortality was 2.9 vs 1.0% (P = 0.92) and admission to ICU 1.0 vs 0.9% (P = 0.66) in patients with and without IE. Significant associations to IE were found for inhalational anaesthetics (OR 2.65; 95% CI: 1.57-4.46), duration of anaesthesia ≥2 hours (OR 1.98; 95% CI: 1.14-3.44) and ASA-score ≥3 (OR 2.74; 95% CI: 1.64-4.57). Conclusion: One of 10 patients had IE as defined by the Nu-DESC score, which was significantly associated with increased LOS. Longer duration of anaesthesia, inhalational anaesthesia and ASA ≥3 were significantly associated to this.