This is a Phase 2, open label, multicenter, study evaluating the efficacy and safety of ABT-199 in relapsed or refractory subjects with CLL harboring 17p13 (TP53 locus) deletion. One hundred seven (107) subjects were enrolled in the main cohort, with evaluation of efficacy as the primary objective, and approximately 50 subjects will be enrolled in the safety expansion cohort to evaluate safety and updated tumor lysis syndrome prophylaxis and management measures. Enrollment into the main cohort is closed. Enrollment into the safety expansion cohort is closed.