Veterinary surgeons are often asked to provide reports to courts describing factual observations and their expert opinion on the presence or absence of unnecessary suffering in animals. This study reviewed 42 expert witness reports in order to describe the approach taken to the assessment of unnecessary suffering. While most reports suitably described factual observations, there was significant variation in the opinions on suffering and the actions of the owner. Severity and duration of potential suffering was commented upon in 26 and 29 reports, respectively. Experts used terms associated with negative mental states and physical states in 28 and 27 reports, respectively. The necessity of suffering was commented upon in 27 reports, with minimal commentary on the actions of the owner. External references supporting the opinion of the expert were only provided in 13 reports. There was evidence of disputes between experts concerning the definition of suffering, the significance of clinical findings and the relevance of different assessment methods. It is suggested that expert witness reports should include a systematic consideration of the animal's mental and physical states, severity of harm, duration of harm and a commentary on the necessity of suffering as defined by legislation.