Identification of patients’ and health professionals’ quality improvement preferences is an essential first step in collaborative improvement models. This includes experience-based codesign (EBCD), where service change is strategically introduced following stakeholder consultation. This study compared the number and types of improvement initiatives selected by outpatients and health professionals. Using electronic surveys designed to inform EBCD studies, 541 outpatients (71.1% consent) and 124 professionals (47.1% response) selected up to 23 general initiatives. On average, outpatients selected 2.4 (median = 1, interquartile range = 1–3) initiatives and professionals selected 10.7 (median = 10; interquartile range = 6–15) initiatives. Outpatients demonstrated a strong preference for improvements to clinic organization, such as appointment scheduling and clinic contact. Outpatients selected relatively fewer initiatives potentially reducing the complexity of service change and resources required to address preferences. Comparatively, professionals indicated a greater degree of change is needed and selected initiatives related to communication with patients and other professionals, including coordinating multidisciplinary care. Improvements to information provision were commonly selected by both groups and offered a strategic opportunity to address patients’ and professionals’ preferences. By quantifying the ways in which preferences differed, this study emphasizes the need for collaborative approaches to health service change and may be used to initiate an informed discussion on patients’ and professionals’ quality improvement preferences in tertiary care.