IMPORTANCE: Older patients undergoing abdominal surgery commonly experience preventable delirium, which extends their hospital length of stay (LOS). OBJECTIVE: To examine whether a modified Hospital Elder Life Program (mHELP) reduces incident delirium and LOS in older patients undergoing abdominal surgery. DESIGN, SETTING, AND PARTICIPANTS: This cluster randomized clinical trial of 577 eligible patients enrolled 377 older patients (≥65 years of age) undergoing gastrectomy, pancreaticoduodenectomy, and colectomy at a 2000-bed urban medical center in Taipei, Taiwan, from August 1, 2009, through October 31, 2012. Consecutive older patients scheduled for elective abdominal surgery with expected LOS longer than 6 days were enrolled, with a recruitment rate of 65.3%. Participants were cluster randomized by room to receive the mHELP or usual care. INTERVENTIONS: The intervention (implemented by an mHELP nurse) consisted of 3 protocols administered daily: orienting communication, oral and nutritional assistance, and early mobilization. Intervention group participants received all 3 mHELP protocols postoperatively, in addition to usual care, as soon as they arrived in the inpatient ward and until hospital discharge. Adherence to protocols was tracked daily. MAIN OUTCOMES AND MEASURES: Presence of delirium was assessed daily by 2 trained nurses who were masked to intervention status by using the Confusion Assessment Method. Data on LOS were abstracted from the medical record. RESULTS: Of 577 eligible patients, 377 (65.3%) were enrolled and randomly assigned to the mHELP (n = 197; mean [SD] age, 74.3 [5.8] years; 111 [56.4%] male) or control (n = 180; mean [SD] age, 74.8 [6.0] years; 103 [57.2%] male) group. Postoperative delirium occurred in 13 of 196 (6.6%) mHELP participants vs 27 of 179 (15.1%) control individuals, representing a relative risk of 0.44 in the mHELP group (95% CI, 0.23–0.83; P = .008). Intervention group participants received the mHELP for a median of 7 days (interquartile range, 6–10 days) and had a shorter median LOS (12.0 days) than control participants (14.0 days) (P = .04). CONCLUSIONS AND RELEVANCE: For older patients undergoing abdominal surgery who received the mHELP, the odds of delirium were reduced by 56% and LOS was reduced by 2 days. Our findings support using the mHELP to advance postoperative care for older patients undergoing major abdominal surgery. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01045330.