['To investigate potential risk factors for delirium in critically ill patients through a meta-analysis of clinical observational studies.', 'A literature search was conducted of MEDLINE and Embase databases. Studies that reported risk factors for delirium in a critical care setting were included. Data were independently extracted by two reviewers and pooled using a fixed-effect or random effects model according to the result of a heterogeneity test.', 'Twenty-five studies were included. The combined odds ratio (95% confidence interval) for each potential risk factor estimated by meta-analysis was as follows (univariate/multivariate): alcohol use, 1.47 (0.79-2.72)/2.34 (1.56-3.49); smoking, 1.01 (0.81-1.25)/1.61 (0.83-3.10); hypertension, 1.64 (1.30-2.06)/1.98 (1.44-2.72); age (per year), 1.03 (1.001-1.05)/1.04 (1.02-1.05); age >65 years, 2.52 (1.55-4.10)/2.59 (1.93-3.47); mechanical ventilation, 3.09 (1.43-6.66)/4.51 (1.41-14.39); and Acute Physiology and Chronic Health Evaluation (APACHE) II score (per point), 1.13 (1.06-1.21) (multivariate only). There was no evidence of publication bias except for APACHE II score.'] Does a meta-analysis of critically ill patients reveal several potential risk factors for delirium?