Context. Rattlesnake bites in Brazil are generally caused by adult individuals, with most of the envenomed patients showing systemic manifestations that include varying degrees of neurotoxicity (acute myasthenia), rhabdomyolysis and coagulopathy, with only mild or no local manifestations. We report a case of envenoming by a juvenile South American rattlesnake (Crotalus durissus terrificus) that involved coagulopathy as the main systemic manifestation. Case details. A 19-year-old male was admitted to our Emergency Department with coagulopathy (incoagulable PT, APTT and INR), no remarkable local manifestations and no signs/symptoms of myasthenia or rhabdomyolysis (serum CK, LDH, ALT and AST within reference levels) 5 days after being bitten by a small snake that was described as a rattlesnake but was not brought for identification at admission. The patient had already been treated in another Emergency Department with i.v. bothropic antivenom (AV) 1 h and 4 days post-bite. Based on the possibility of an unusual rattlesnake bite, crotalic AV was administered i.v., which improved the coagulation (9 h post-CroAV, INR = 2.11; 36 h post-CroAV, INR = 1.42). During hospitalization, relatives brought the snake that caused the bite, which was identified as a 38-cm long C. d. terrificus. Discussion. Little is known about the clinical manifestations after bites by juvenile C. d. terrificus. This case shows that systemic envenoming by juvenile C. d. terrificus may result in coagulopathy as the main systemic manifestation, without neuromyotoxic features normally associated with bites by adult specimens. Despite the delayed administration, crotalic AV was effective in improving the blood coagulation.516505508