Computed tomographic (CT) scans and clinical data were reviewed in 21 patients with significant hematoma occurring after catheterization. The procedures included percutaneous transluminal coronary angioplasty (n = 15), cardiac catheterization (n = 2), peripheral angioplasty (n = 2), valvuloplasty (n = 1), and venous access catheterization (n = 1). Clinical data including medications, transfusion requirements, and sequelae were obtained by reviewing the patients' charts. Four distinct types of postcatheterization bleeding were identified at CT: retroperitoneal, intraperitoneal, groin and thigh, and abdominal wall hematomas. CT scans contributed to treatment in all patients by helping indicate the need for more intensive monitoring and by helping predict the potential need for surgery. Sequelae included the need for blood transfusions in 17 patients (mean of 5 units of blood in each patient receiving transfusion) and surgery in two patients for vessel repair.