INTRODUCTION: After discovering a low incidence of delirium for hip fracture patients at our institution, we evaluated if this was due to underreporting and, if so, where process errors occurred. METHODS: Hip fracture patients aged ≥ 60 with a diagnosis of delirium were identified. Chart-Based Delirium Identification Instrument (CHART-DEL) identified missed diagnoses of delirium. Process maps were created based off staff interviews and observations. RESULTS: The incidence of delirium was 15.3% (N = 176). Within a random sample (n = 98), 15 patients (15.5%) were diagnosed, while 20 (24.7%) went undiagnosed despite evidence of delirium. Including missed diagnoses, delirium prevalence was higher in the sample compared to all patients (35.7% vs 15.3%, p < 0.001). Most missed diagnoses were due to failure in identifying delirium (60%) or failure in documenting/coding diagnosis (20%). The prevalence of baseline cognitive impairment was higher in undiagnosed delirium patients versus correctly diagnosed patients (80% vs 20%, p = 0.001). CONCLUSIONS: Our institution significantly underreports delirium among hip fracture patients mainly due to; (1) failure to identify delirium by the clinical staff, and (2) failure to document/code diagnosis despite correct identification. Baseline cognitive impairment can render delirium diagnosis challenging. These serve as targets for quality improvement and hip fracture care enhancement.