In response to multiple incidents of registration-associated patient misidentification (eg, assigning a new patient an existing patient's medical record number), an interdisciplinary team used plan-do-study-act methodology to investigate the root cause of such errors and formulate solutions. Several system problems were identified, ranging from inadequate training of registrars to the lack of a true master list of patients' medical record numbers. The authors describe the iterative process used to identify and address sources of error at several points within the patient registration process.