It is recommended that critically ill patients undergo routine delirium monitoring with a valid and reliable tool such as the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU). However, the validity and reliability of the Arabic version of the CAM-ICU has not been investigated. Here, we test the validity and reliability of the Arabic CAM-ICU.We conducted a psychometric study at ICUs in a tertiary-care hospital in Saudi Arabia. We recruited consecutive adult Arabic-speaking patients, who had stayed in the ICU for at least 24 hours, and had a Richmond Agitation-Sedation Scale (RASS) score ≥ - 2 at examination. Two well-trained examiners (ICU nurse and intensivist) independently assessed delirium in eligible patients with the Arabic CAM-ICU. Evaluations by the two examiners were compared with psychiatrist blind clinical assessment of delirium according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Subgroup analyses were conducted for age, invasive mechanical ventilation, and gender.We included 108 patients (mean age: 62.6 ± 17.6; male: 51.9%), of whom 37% were on invasive mechanical ventilation. Delirium was diagnosed in 63% of enrolled patients as per the psychiatrist clinical assessment. The Arabic CAM-ICU sensitivity was 74% (95% confidence interval [CI] = 0.63-0.84) and 56% (95%CI = 0.44-0.68) for the ICU nurse and intensivist, respectively. Specificity was 98% (95%CI = 0.93-1.0) and 92% (95%CI = 0.84-1.0), respectively. Sensitivity was greater for mechanically-ventilated patients, women, and those aged ≥65 years. Specificity was greater for those aged < 65 years, non-mechanically-ventilated patients and men. The median duration to complete the Arabic CAM-ICU was 2 min (interquartile range, 2-3) and 4.5 min (IQR, 3-5) for the ICU nurse and intensivist, respectively. Inter-rater reliability (kappa) was 0.66.The Arabic CAM-ICU demonstrated acceptable reliability and validity to assess delirium in Arabic-speaking ICU patients.