A 40-year-old Caucasian man diagnosed with right deep venous thrombosis secondary to trauma was treated with subcutaneous enoxaparin. Within minutes of administering the first dose (1 mg/kg), he experienced an apparent anaphylactoid reaction; symptoms were abdominal pruritus, severe cough, shortness of breath, anxiety, and global pruritus. Physical examination revealed an erythematous macular rash and stridor on auscultation secondary to cervical edema. No other drugs were given before the reaction occurred, and the patient's only drug therapy at home had consisted of a daily multivitamin, and acetaminophen and ibuprofen as needed. Administration of low-molecular-weight heparins such as enoxaparin is increasing, and clinicians must be aware of the potential for adverse drug events such as hypersensitivity reactions.