A pragmatic agreed definition of adverse events in manual therapy is required to explore incidence and prevalence. We aimed to identify and describe such adverse events and seek a consensus definition. A focus group identified issues surrounding the definition of adverse events and generated the content for a questionnaire. This questionnaire was used to conduct a modified Delphi consensus survey with an expert panel (n=50). Consensus was defined as >74% agreement. Three consensus rounds were executed. There was a 50% response rate for round one, 62% for round two and 55% for round three. A layered pragmatic definition was agreed: 'Major' adverse events are medium to long term, moderate to severe and unacceptable, they normally require further treatment and are serious and distressing; 'Moderate' adverse events are as 'major' adverse events but only moderate in severity; and 'Mild' and 'not adverse' adverse events are short term and mild, non-serious, the patient's function remains intact, and they are transient/reversible; no treatment alterations are required because the consequences are short term and contained. We concluded that classifying adverse events was difficult without context or detail. Classification may be improved by using the taxonomy and descriptions suggested in this study.