Rare, serious, and common, benign adverse events (AE) are associated with MT techniques. A proposed standard for defining AE in manual therapy (MT) practise has been published but it did not include the patient perspective. Research comparing clinician and patient reporting of AE demonstrates that several differences exist; for example, the reporting of objective versus subjective events. The objective of this study was to describe how patients define AE associated with MT techniques. A descriptive qualitative design was employed. Semi-structured interviews were used with a purposive sample of patients (n = 13) receiving MT, from physiotherapy, chiropractic and osteopathic practises in Ontario, Canada. The interview guide was informed by existing evidence and consultation with content and methodological experts. Interviews were audiotaped and transcribed verbatim. Date were analysed by two independent team members using thematic content analysis. A key finding was that patients defined mild, moderate and major AE by pain/symptom severity, functional impact, duration and by ruling out of alternative causes. An overarching theme identified multiple factors that influence how the AE is perceived. These concepts differ from the previously proposed framework for defining AE that did not include the patient perspective. Future processes to create standard definitions or measures should include the patient viewpoint to provide a broader, client-centred foundation.