Under study were two hundred and forty nine cases of accidents caused by South American rattlesnakes (Crotalus durissus) admitted to the Vital Brasil Hospital, São Paulo, Brasil, from 1974 to 1990. The accidents were more common in the afternoon, from January to April and from October to December. Ninety nine out of 100 snakes classified as subspecies were C. d. terrificus. Most of the patients were males (80.7%). The inferior and superior limbs were bitten in 66.4% and 29.2% of the cases, respectively. The more frequent clinical manifestations were pain (61.0%) and edema (55.0%) at site of the bite, palpebral ptosis (75.9%), darkening of the urine due to myo-globinuria (38.6%) and myalgia (36.1%). Nine (3.6%) out of 32 patients with acute renal failure were submitted to dialysis, three presented respiratory failure treated with intubation and/or tracheotomy and one presented an ischemic cerebral stroke. Alteration of the blood coagulation was present in 48.1% of the patients. The blood picture of some patients several hours after the accident showed leuco-cytosis with a left shift and a tendency to normal values with eosinophilia. Serum creatinekinase activity was increased in 20 of 21 patients, with higher values 24 hours after the bite reaching 2,377 times the reference value. Lethality was 0.8%.