Reports on bleeding tendencies in osteogenesis imperfecta (OI) are rare in the literature. Abnormalities are attributed to a defect in the vessel wall. In a prospective study of 36 patients with known OI, we used the thrombo-elastogram (TEG) to survey haemostatic competence. TEG, which can indicate the nature of a haemostatic defect within an hour, provides a graphic representation of clotting. The study was conducted from July 2000 to April 2001. The ages of the 18 male and 18 female patients ranged from 9 months to 21 years (mean 10.7 years). Three had type-I OI, 27 type-III and six type-IV. Blood specimens were taken according to a TEG protocol and, to correlate with other bleeding tests, specimens were analysed for platelet count, prothrombin time (PT) and partial thromboplastin time (PTT). Platelet counts were normal in all patients. PT and PTT were normal in all but one patient. When TEG results were compared with standard values, 30 patients had normal results, four had increased coagulation and two had a decreased coagulable state directly attributed to platelet defects. Haemostatic defects in OI may be due to platelet function abnormalities. TEG, an inexpensive, simple, sensitive and reliable screening instrument, should be used before surgery to identify bleeding tendencies in OI patients.