A method of classification for hematomas of the rectus abdominis sheath (RSH) is proposed based on findings observed in CT in the 13 cases of RSH in the present study. Type I hematomas (five cases) are slight and do not require hospitalization. Type II (three cases) and type III (five cases) are moderate and severe hematomas, respectively, and do require hospitalization. The patients with type III hematomas were all undergoing anticoagulant therapy and presented with a picture of acute abdomen, and in all five cases blood transfusion was carried out. Ultrasonography and, in particular, CT permitted a correct diagnosis of RSH. RSH should be considered (anticoagulant therapy induced) in females with sudden abdominal pain to avoid unnecessary surgical intervention.