BACKGROUND: Negative veterinary client complaint behaviour poses wellbeing and reputational risks. Adverse events are one source of complaint. Identifying factors that influence adverse event-related complaint behaviour is key to mitigating detrimental consequences and harnessing information that can be used to improve service quality, patient safety and business sustainability. METHODS: Interviews were conducted with five veterinary client complainants and five veterinary client mediators. Qualitative content analysis of the transcripts was used to identify categories of capability, opportunity and motivation influencing client behaviour. One category of motivation identified focused on the desired outcomes of complainants. Two hundred and eighty resolved veterinary‒client mediation cases related to adverse events subsequently underwent content analysis to quantify these desired outcomes. RESULTS: Client complaint behaviour was motivated by clients' emotional reactions, perceptions and beliefs and desire to achieve an outcome as a result, and was influenced by previous complaint experience, technological ability, self-confidence and broader organisational and societal factors. Although financial redress was the most commonly identified desired outcome, apology, honesty, accountability and prevention of future events were valued. LIMITATIONS: Small data sets and interpretative analyses limit the generalisability of the findings. CONCLUSIONS: Proactively engaging clients in relation to adverse events is likely to reduce negative complaint behaviour and facilitate veterinary quality improvement.