Severe factor XI deficiency is defined by levels of <0.20 IU/mL. Such individuals have a high probability of post-operative hemorrhage. Individuals with levels between 0.20 IU/mL and the lower limit of the normal range, generally 0.65-0.80 IU/mL, are generally classified as having partial or mild deficiency with a lower risk of post-operative bleeding. Partial deficiency is being increasingly recognized following pre-operative tests or as a result of family screening. Thus partial factor XI deficiency is often diagnosed in asymptomatic individuals, creating management dilemmas because of the unpredictability of the bleeding risk. To differentiate an isolated or combined bleeding disorder in a patient with factor XI deficiency, other causes of bleeding should be investigated and excluded (e.g. von Willebrand disease, platelet disorders).