Whilst common clinical manifestations of type 1 Gaucher disease (GD1) include hepatosplenomegaly, peripheral blood cyotpenias and bone disease, a bleeding diathesis has also been reported in some patients. The pattern and severity of bleeding and their role in the clinical presentation of GD1 are not well characterised. Within our single centre cohort of 86 GD1 patients, 46 (53.4%) of patients had bleeding symptoms at presentation with bleeding being the primary presenting symptom in 16 (18.6%). The commonest bleeding symptom was bruising (45% of entire cohort) but post-operative bleeding was reported in 8%. More detailed assessment of the nature and severity of bleeding symptoms was undertaken in 40 GD1 and 47 controls using the MCMDM-1 bleeding states questionnaire. This demonstrates that GD1 results in mucocutaneous bleedingwith a score≥4, predictive of a haemostatic defect, in 47.5% of patients; only one control had a bleeding score ≥4. Bleeding events in GD1 occurred across the spectrum of mucocutaneous sites (epistaxis, menorrhagia, cutaneous, post-operative, post-partum) but no joint, intracerebral or gastrointestinal bleeding was reported. There was no correlation between bleeding score or reported bleeding symptoms and platelet count. Median bleeding scores were higher in those with an abnormal coagulation screen (PT or APTT) at baseline compared to thosewith a normal screen (4 vs. 2, p = 0.06). There was no correlation between bleeding severity and the severity of GD1 diseasemanifestations overall (baseline Zimran severity score index) or in other manifestations which have previously been hypothesised to have similar underlying mechanisms to the bleeding diathesis (bone infarcts and gammopathies). Within the cohort, 17 patients had been identified as FXI deficient based on reduced FXI activity pre-enzyme replacement therapy (ERT), measured either due to investigation of bleeding symptoms or investigation of an abnormal coagulation screen. Five of these patients had been reviewed in haemophilia centres prior to diagnosis of GD1 and been given a diagnosis of inherited FXI deficiency on the basis of reduced enzyme activity. FXI activity significantly improved following ERT (mean baseline 55 IU/dL vs. follow up 90 IU/dL, p b 0.0001, n = 13). F11 gene sequencing performed on 6 patients (3 with persistently low FXI activity and 3 with reduced FXI activity commenced on ERT within the previous 12 months) was normal. This study demonstrates that mucocutaneous bleeding, severe enough to result in presentation to haemostasis specialists occurs in approximately 50% of patients with GD1. Bleeding symptoms may be indistinguishable from those of patientswith othermild bleeding disorders and there is a risk of misor insufficient diagnosis. Physicians treating GD1 should raise awareness of this presentation amongst their haemostasis colleagues to enable prompt arrival at the correct diagnosis. FXI deficiency in GD1 arises as an acquired coagulation defect due to the GD1, not co-inheritance of F11 gene mutations and usually responds to ERT. Comprehensive reassessment of haemostatic defects should be undertaken in GD1 patients with history of prior bleeding requiring surgical interventions as the defect may have improved following institution of ERT.