BACKGROUND: Praziquantel (PZQ) is the recommended treatment for managing human Schistosomiasis. This drug commonly causes transient adverse effects such as headache, dizziness, nausea, diarrhea, and abdominal pain. Hypersensitive reactions are rare, with only 7 cases have been reported worldwide. A 13-year-old Brazilian female suffered anaphylaxis after taking PZQ to treat Schistosomiasis mansoni, the first case reported in Brazil. CASE DESCRIPTION: The patient was a 13-year-old-female from Conde, Bahia, Brazil. She was screened by an infectious disease doctor, and the intake of 60mg/Kg PZQ was indicated. Previous hypersensitivity to the medication was denied. However, about an hour later, the patient reported rash and generalized edema, evolving into dizziness and somnolence. Fexofenadine (120mg) was administered, and she was taken to the local family health unit. At arrival, the patient presented with tachycardia (131 bpm), dyspnea (27 BPM), somnolence, and worsening saturation (90%), and 20mg prednisone were administered. Forty minutes after, the patient evolved with sudoresis and hypotension, and 0.6ml (0.01mg/kg) of epinephrine was administered intramuscularly. The patient was transferred to a hospital, and upon arrival, she presented hypotension, sudoresis, and altered mental status. She received venous access, and oxygenation and evolved with a good prognosis, being discharged the next day. DISCUSSION: The present case demonstrated symptoms compatible with anaphylaxis, such as skin rash, dyspnea, tachycardia, worsening saturation, and generalized edema, an hour after PZQ ingestion. This drug can sometimes cause hypersensitivity reactions induced by a sudden antigen released from hatched schistosome eggs and dying worms. However, since PZQ’s TMax is 2 hours, that would be a much later response compared to this case. The immediate post-ingestion response suggests that it was due to drug allergy. CONCLUSION: Although hypersensitivity reactions to PZQ are rare, they can be associated with severe symptoms and outcomes. Therefore, health professionals should be aware of this lifethreatening adverse effect.