Background and Objectives Delirium creates distinct emotional distress in patients and family caregivers, yet there are limited tools to assess the experience. Our objective was to develop separate patient and family caregiver delirium burden instruments and to test their content and construct validity. Research Design and Methods Two hundred forty-seven patients and 213 family caregivers were selected from an ongoing prospective cohort of medical-surgical admissions aged ≥70 years old. New patient and family caregiver delirium burden instruments were developed and used to measure the subjective experiences of in-hospital delirium. Delirium and delirium severity were measured by the Confusion Assessment Method (CAM) and CAM-Severity (long form). Results Both Delirium Burden (DEL-B) instruments consist of eight questions and are measured on a 0 – 40 point scale. Final questions had good clarity and relevancy, as rated by the expert panel, and good internal consistency (Cronbach's α =.82–.86). In the cohort validation, Patient DEL-B (DEL-B-P) was 5.1 points higher and Family Caregiver DEL-B (DEL-B-C) was 5.8 points higher, on average, for patients who developed delirium compared to those who did not (p <.001). Test–retest reliability of DEL-B-C at baseline and 1 month was strong (correlation =.73). Delirium severity was mildly-moderately correlated with DEL-B-P (correlation =.34) and DEL-B-C (correlation =.26), suggesting contribution of other factors. Discussion and Implications We created instruments to reliably measure and evaluate the burden of delirium for patients and their family caregivers. Although additional validation is indicated, these instruments provide a key first step toward measuring and improving the subjective experience of delirium for patients and their families.