This study questioned whether manual lung hyperinflation (MHI) and postural drainage reduced the incidence of nosocomial pneumonia or improved other outcome variables in mechanically ventilated trauma patients. Patients were withdrawn from the study if they developed nosocomial pneumonia according to a predetermined definition or on the clinical suspicion of nosocomial pneumonia by the attending intensivist. Of the 46 patients who fulfilled all the inclusion criteria and were enrolled into the study, 22 patients were randomized to group A (physiotherapy) and 24 patients to group B (control group). Twice as many patients were withdrawn in group B (8/24) compared with group A (4/22), although the differences were not statistically significant, [X2(1, 1) = 1.36, P = 0.24]. The length of time receiving mechanical ventilation and in the ICU was similar between the two groups and there were no differences in pulmonary dysfunction ("worst" daily PaO2/FiO2 ratio) between the two groups. There were no ICU deaths in either group. Physiotherapy as used in this study was not associated with a reduced incidence of nosocomial pneumonia based on standard clinical criteria. Nevertheless the trend to more frequent nosocomial pneumonia in the control patients suggests that a larger study in more severely injured patients with stricter clinical criteria for the definition of nosocomial pneumonia is indicated.