To describe our experience in the diagnosis and treatment of haematoma of the rectus abdominis.Retrospective study.St. Antonius Hospital, Nieuwegein, The Netherlands.40 patients treated between 1976 and 1991 for haematoma of the rectus abdominis muscle.Correct diagnosis and treatment of the haematoma.The mean age of the patients was 63 years (range 31-83), and just over half were women. Predisposing factors included the use of anticoagulant drugs (n = 30, 75%), the presence of scars on the abdominal wall (n = 27, 68%), the haematoma had been provoked by coughing (n = 24, 60%), and coexistent cardiovascular disease (n = 22, 55%). Nineteen of the haematomas were in the right lower quadrant and 15 in the left; in only four was the upper part of the rectus muscle affected. Eight patients had bled severely enough to require blood transfusion, and 32 were successfully treated conservatively.The single most important factor in the diagnosis of haematoma of the rectus abdominis is awareness of its existence; it should be included as a differential in all patients who present with an acute abdomen. Once the diagnosis has been confirmed (by ultrasonography or computed tomography) patients should be treated conservatively as those that are operated on are at risk of developing complications.