Safety data were evaluated in 240 patients with previously-treated CLL who were treated with single-agent venetoclax at a target dose of 400 mg orally daily. The most common (greater than or equal to 20%) adverse reactions of any grade were neutropenia, diarrhea, nausea, anemia, upper respiratory tract infection, thrombocytopenia, and fatigue. Serious adverse reactions were reported in 44% of patients, and the most common (greater than or equal to 2%) serious adverse reactions were pneumonia, febrile neutropenia, pyrexia, autoimmune hemolytic anemia, anemia, and tumor lysis syndrome (TLS).