In a review and meta-analysis conducted in 1993, psychological preparation was found to be beneficial for a range of outcome variables including pain, behavioural recovery, length of stay and negative affect. Since this review, more detailed bibliographic searching has become possible, additional studies testing psychological preparation for surgery have been completed and hospital procedures have changed. The present review examines whether psychological preparation (procedural information, sensory information, cognitive intervention, relaxation, hypnosis and emotion-focused intervention) has impact on the outcomes of postoperative pain, behavioural recovery, length of stay and negative affect. Objectives To review the effects of psychological preparation on postoperative outcomes in adults undergoing elective surgery under general anaesthetic. Search methods We searched the Cochrane Register of Controlled Trials (CENTRAL 2014, Issue 5), MEDLINE (OVID SP) (1950 to May 2014), EMBASE (OVID SP) (1982 to May 2014), PsycINFO (OVID SP) (1982 to May 2014), CINAHL (EBESCOhost) (1980 to May 2014), Dissertation Abstracts (to May 2014) and Web of Science (1946 to May 2014). We searched reference lists of relevant studies and contacted authors to identify unpublished studies. We reran the searches in July 2015 and placed the 38 studies of interest in the ‘awaiting classification’ section of this review. Psychological preparation and postoperative outcomes for adults undergoing surgery under general anaesthesia (Review) 1 Copyright © 2016 The Cochrane Collaboration. Published by JohnWiley & Sons, Ltd. Selection criteria We included randomized controlled trials of adult participants (aged 16 or older) undergoing elective surgery under general anaesthesia. We excluded studies focusing on patient groups with clinically diagnosed psychological morbidity. We did not limit the search by language or publication status.We included studies testing a preoperative psychological intervention that included at least one of these seven techniques: procedural information; sensory information; behavioural instruction; cognitive intervention; relaxation techniques; hypnosis; emotion-focused intervention. We included studies that examined any one of our postoperative outcome measures (pain, behavioural recovery, length of stay, negative affect) within one month post-surgery. Data collection and analysis One author checked titles and abstracts to exclude obviously irrelevant studies. We obtained full reports of apparently relevant studies; two authors fully screened these. Two authors independently extracted data and resolved discrepancies by discussion. Where possible we used random-effects meta-analyses to combine the results from individual studies. For length of stay we pooled mean differences. For pain and negative affect we used a standardized effect size (the standardized mean difference (SMD), or Hedges’ g) to combine data from different outcome measures. If data were not available in a form suitable for meta-analysis we performed a narrative review. Main results Searches identified 5116 unique papers; we retrieved 827 for full screening. In this review, we included 105 studies from 115 papers, in which 10,302 participants were randomized.Mainly as a result of updating the search in July 2015, 38 papers are awaiting classification. Sixty-one of the 105 studies measured the outcome pain, 14 behavioural recovery, 58 length of stay and 49 negative affect. Participants underwent a wide range of surgical procedures, and a range of psychological components were used in interventions, frequently in combination. In the 105 studies, appropriate datawere provided for themeta-analysis of 38 studiesmeasuring the outcome postoperative pain (2713 participants), 36 for length of stay (3313 participants) and 31 for negative affect (2496 participants). We narratively reviewed the remaining studies (including the 14 studies with 1441 participants addressing behavioural recovery). When pooling the results for all types of intervention there was low quality evidence that psychological preparation techniques were associated with lower postoperative pain (SMD -0.20, 95% confidence interval (CI) -0.35 to -0.06), length of stay (mean difference -0.52 days, 95% CI - 0.82 to -0.22) and negative affect (SMD -0.35, 95% CI -0.54 to -0.16) compared with controls. Results tended to be similar for all categories of intervention, although there was no evidence that behavioural instruction reduced the outcome pain. However, caution must be exercised when interpreting the results because of heterogeneity in the types of surgery, interventions and outcomes. Narratively reviewed evidence for the outcome behavioural recovery provided very low quality evidence that psychological preparation, in particular behavioural instruction, may have potential to improve behavioural recovery outcomes, but no clear conclusions could be reached. Generally, the evidence suffered from poor reporting, meaning that few studies could be classified as having low risk of bias. Overall,we rated the quality of evidence for each outcome as ‘low’ because of the high level of heterogeneity in meta-analysed studies and the unclear risk of bias. In addition, for the outcome behavioural recovery, too few studies used robust measures and reported suitable data for meta-analysis, so we rated the quality of evidence as ‘very low’. Conclusions The evidence suggested that psychological preparation may be beneficial for the outcomes postoperative pain, behavioural recovery, negative affect and length of stay, and is unlikely to be harmful. However, at present, the strength of evidence is insufficient to reach firm conclusions on the role of psychological preparation for surgery. Further analyses are needed to explore the heterogeneity in the data, to identify more specifically when intervention techniques are of benefit.