To test whether an interactive voice response (IVR) system phone call was equally effective as a nurse-delivered phone call at educating and preparing patients for flexible sigmoidoscopy (FS) and colonoscopy examinations.Three-arm randomized controlled trial.The trial included patients with upcoming FS or colonoscopy appointments to test the equivalence of an IVR system to nurse-delivered phone calls in reducing appointment nonattendance and inadequate preparation for an examination. Message timing and satisfaction with the intervention were assessed. The 3 study conditions included the following: nurse phone call 7 days before the procedure, IVR system call 7 days before the procedure, and IVR system call 3 days before the procedure. All calls included an appointment reminder, information about preparation for the examination, and encouragement to prepare for and attend the examination.A total of 3610 patients were eligible for the study; of these, 1229 (34%) were scheduled for FS and 2381 (66%) for colonoscopy. There were no statistically significant differences across the 3 study arms in appointment attendance or adherence to preparation instructions. Significantly more patients in IVR conditions reported neutral perceptions about the phone calls, and more patients receiving nurse calls reported very positive perceptions about the phone calls.An IVR system call is as effective as a nurse phone call for ensuring that patients attend appointments and are adequately prepared for endoscopy examinations.