INTRODUCTION: Uncertainty is a common experience in the complex adaptive health system, particularly amongst mental health professionals structured for the delivery of integrated care. Increased understanding of uncertainty will not necessarily make things more certain, but can act to sensitize professionals to the challenges they face. The aim of this study is to examine the types and situations of uncertainty experienced by professionals working in a mental health setting based on an integrated care model. The research assesses the impact of experience and professional group on reported uncertainties. METHODS: First, semi-structured interviews were undertaken with clinical and non-clinical staff to examine uncertainties experienced by professionals working in headspace centres in Australia. Second, an online survey was conducted to quantify the experiences of uncertainty and explore associations. RESULTS: Findings revealed three overarching and largely interrelated aspects of uncertainty, namely: decision-making; professional role; and external factors. Most commonly, staff reported experiences of uncertainty pertaining to deciding to accept a client into the service and then deciding how to treat them. This is often due to arbitrary, or overly-restrictive criteria in integrated care. Findings also suggested that uncertainty does not necessarily decline with experience and there were no significant differences in levels of uncertainty between clinical and non-clinical staff. CONCLUSIONS: This study highlights the importance of acknowledging uncertainties and actively clarifying role ambiguities when working alongside diverse professionals in mental health care.