Iliopsoas haemorrhage in patients with bleeding disorders is a potentially life-threatening condition, with significantly associated morbidity. Despite its clinical importance, little has been published on the frequency, complications or outcomes of this entity since the advent of modern therapies for haemophilia. In a retrospective review of 297 patients with bleeding disorders followed at our centre, we identified 46 episodes of iliopsoas haemorrhage in 31 patients. Patients presented primarily with thigh, hip and/or groin pain, and frequently had flexion hip contracture, femoral nerve paresthesia, and >2 g dL(-1) haemoglobin drop. The duration of symptoms prior to seeking medical attention was 3.8 +/- 4 days. Nineteen of 155 patients (12.3%) with haemophilia A had 28 episodes of iliopsoas bleed; 52.6% of these patients had severe haemophilia. Of these 19 patients with haemophilia A who had iliopsoas haemorrhage, seven (36.8%) had an inhibitor to factor VIII (FVIII), and accounted for one-half of the bleeding episodes. Nine of 66 patients (13.6%) with haemophilia B had 15 episodes of iliopsoas haemorrhage; 22.2% of these patients had severe haemophilia, including one patient with an inhibitor to FIX who had two iliopsoas bleeds. The mean duration of therapy was 18.7 +/- 11.9 days, and the duration of hospitalization was 12.3 +/- 9.1 days. The length of hospital stay was significantly longer in patients with inhibitors, when compared with patients without inhibitors (19.1 +/- 5.8 days vs. 7.6 +/- 7.8 days; P<0.0001) with higher factor consumption, although the total duration of therapy was not significantly different. Patients with inhibitors were over-represented in the cohort of haemophiliacs with iliopsoas bleed. Patients with inhibitors who had iliopsoas bleeds remained hospitalized longer, although the duration of therapy was the same as patients with no inhibitors. There was a low frequency of recurrent bleed (2.8%).