A 25-year-old male, white, with severe hemophilia B (F.IX < 1%) developed a rash of small erythematous macules, purpuric spots and petechia on the lower extremities. These skin lesions were discrete, not pruritic, not papular and with no areas of necrosis. No relationship to previous infection was determined. As the patient did not present any other clinical alteration, he was observed daily on an ambulatory basis in a four days’ period, without any medication. On the fifth day parallel to the disappearance of the skin lesions, the patient began to complain of abdominal pain, in crisis of moderate intensity. As the abdominal discomfort increased rapidly on the following 24 hours, we introduced specific therapy on an in-patient basis. The case evolved to an acute abdominal picture that required surgical intervention. The laparathomy resulted in large ressections of jejunum and ileum that showed large hemmorrhagic and necrotic areas. The post-operative period elapsed without incidents and the patient left the hospital in three weeks. This case that at the beginning could not give us a clear diagnosis of an anaphylactoid purpura shows us once more that in hemophilia, we must transfuse as early as possible.