BTK and B-cell chronic lymphocytic leukemia: Ibrutinib, a first‐in‐class, once‐daily inhibitor of Bruton's tyrosine kinase (BTK), is approved in the United States for treatment of CLL/SLL.9 Clinical studies indicate that use of ibrutinib and other BTK inhibitors is associated with platelet dysfunction and increased bleeding risk.10, 11, 12, 13, 14, 15, 16, 17 In order to put ibrutinib into a clinical context, it is important to understand incidence of and risk factors for major hemorrhage in the CLL patient population before ibrutinib is widely used.