Question: How often do adverse events (including adverse physiological changes) occur during physiotherapy intervention in intensive care?, Design: A multi-centre prospective observational study., Participants: Five tertiary level university-affiliated intensive care units., Outcome Measures: All physiotherapy intervention in five intensive care units over a three month period. When certain specified changes occurred during physiotherapy intervention, details were noted including diagnosis of patient, intervention, vital signs, radiological changes, co-morbidities, chemical pathology, and fluid balance., Results: 12 281 physiotherapy interventions were completed with 27 interventions resulting in adverse physiological changes (0.2%). This incidence was significantly lower than a previous study of adverse physiological changes (663 events in 247 patients over a 24-hour period); the incidence during physiotherapy intervention was lower than during general intensive care. Common factors in the patients who had an adverse physiological change were a deterioration in cardiovascular status (ie, decrease in blood pressure or arrhythmia) in patients on medium to high doses of inotropes/vasopressors, unstable baseline hemodynamic values, previous cardiac co-morbidities and intervention consisting of positive pressure or right side lying., Conclusion: The incidence of adverse events during physiotherapy intervention in these five tertiary hospitals was low, demonstrating that physiotherapy intervention in intensive care is safe.