There has been considerable uncertainty about the risks and severity of tetanus after intramuscular quinine, a widely used treatment of severe malaria in the rural tropics. We have compared the clinical features and outcome of tetanus in which injection was the only apparent site of infection with tetanus acquired by other routes in patients admitted to the Centre for Tropical Diseases, Ho Chi Minh City, Vietnam. In 1081 consecutive patients with tetanus treated between Jan 26, 1989, and May 27, 1991, 27 followed intramuscular quinine and 15 followed injections of other drugs. Overall mortality was 26% (285/1081). Mortality in patients who had not had preceding injections was 24% (250/1039) compared with 96% (26/27) in the quinine group (relative risk 4.0, 95% CI 3.5-4.6) (p < 0.0001), and 60% (9/15) in the other injections group (2.5, 1.6-3.8) (p < 0.005). 21 patients (78%) in the quinine group died within 72 h of admission compared with 5 (33%) in the other intramuscular injections group (p < 0.01) and 4 (7%) of 54 matched controls (p < 0.0001). Tetanus that follows intramuscular injections has a poor prognosis, but when it follows intramuscular quinine it is usually rapidly fatal.