Objective Delirium is a serious and common complication among older hospitalized patients and is a predictor of many adverse outcomes. However, up to 72% of delirium incidents are unrecognized or misdiagnosed. The aim of this systematic review is to determine the validity, reliability, and feasibility of instruments for the detection of delirium in older hospitalized patients. Methods A systematic literature search was conducted. The inclusion criteria were a mean or median age of 65+ years, the use of the Diagnostic and Statistical Manual of Mental Disorders or International Classification of Diseases‐10 as a reference standard, and publication in English. All included studies underwent a quality assessment (QUADAS‐2). Results Forty‐three of the 3.790 identified studies were relevant to the review, describing 28 instruments. Quality assessment resulted in 37 studies with a positive quality assessment, describing 23 instruments. Five instruments (Delirium Observation Scale (DOS), Nursing Delirium Screening Scale (Nu‐DESC), Confusion Assessment Method (CAM), CAM‐Intensive Care Unit (ICU), and Delirium Rating Scale‐Revised‐98) were described in three or more methodologically sound studies. The Delirium Observation Screening Scale (DOS) and Nu‐DESC are observational instruments with good psychometric properties, but the Nu‐DESC is shorter and has been validated in more languages. The CAM, CAM‐ICU, and Delirium Rating Scale‐Revised‐98 (DRS‐R‐98) are instruments with both observational and interactive components. The CAM is the most widely studied and demonstrates the best psychometric properties. Conclusion Timely detection of delirium might reduce the negative outcomes of delirium in the long term. The Nu‐DESC and CAM appear to be the most adequate instruments for detecting delirium. Copyright © 2016 John Wiley & Sons, Ltd.