Tetanus remains common in many low- and middle-income countries, but as critical care services improve, mortality from tetanus is improving. Nevertheless, patients develop severe syndromes associated with autonomic nervous system disturbance (ANSD) and the requirement for mechanical ventilation (MV). Understanding factors associated with worse outcome in such settings is important to direct interventions. In this study, we investigate risk factors for disease severity and long-term physical outcome in adults with tetanus admitted to a Vietnamese intensive care unit. Clinical and demographic variables were collected prospectively from 180 adults with tetanus. Physical function component scores (PCS), calculated from Short Form Health Survey (SF-36), were assessed in 79 patients at hospital discharge, 3 and 6 months post discharge. Age, temperature, heart rate, lower peripheral oxygen saturation (SpO ) and shorter time from first symptom to admission were associated with MV (OR 1.03 95% confidence interval (CI) 1.00, 1.05, p = 0.04; OR 2.10 95% CI 1.03, 4.60, p = 0.04; OR 1.04 95% CI 1.01, 1.07, p = 0.02); OR 0.80 95% CI 0.66, 0.94, p = 0.02 and OR 0.65 95% CI 0.52, 0.79, p < 0.001, respectively). Heart rate, SpO and time from first symptom to admission were associated with ANSD (OR 1.03 95% CI 1.01, 1.06, p < 0.01; OR 0.95 95% CI 0.9, 1.00, p = 0.04 and OR 0.64 95% CI 0.48, 0.80, p < 0.01, respectively). Median interquartile range PCS at hospital discharge, 3 and 6 months were 32.37 24.95-41.57, 53.0 41.6-56.3 and 54.8 51.6-57.3, respectively. Age, female sex, admission systolic blood pressure, admission SpO , MV, ANSD, midazolam requirement, hospital-acquired infection, pressure ulcer and duration of ICU and hospital stay were associated with reduced 0.25 quantile PCS at 6 months after hospital discharge. MV and ANSD may be suitable endpoints for future research. Risk factors for reduced physical function at 3 months and 6 months post discharge suggest that modifiable features during hospital management are important determinants of long-term outcome.