The phase II CAVALLI (NCT02055820) study assessed efficacy and safety of venetoclax, a selective, B-cell lymphoma-2 (Bcl-2) inhibitor, with rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) in first-line (1L) diffuse large B-cell lymphoma (DLBCL), including patients demonstrating Bcl-2 protein overexpression by immunohistochemistry (Bcl-2 IHC-positive). Eligible patients ≥18 years with previously untreated DLBCL, Eastern Cooperative Oncology Group performance status ≤2, and International Prognostic Index 2-5. Venetoclax 800 mg (days 4-10, cycle 1 and days 1-10, cycles 2-8) was administered with rituximab (8 cycles) and CHOP (6-8 cycles); 21-day cycles. Primary endpoints: safety, tolerability, and complete response (CR) at end of treatment (EOT). Secondary endpoints: progression-free survival (PFS) and overall survival. Comparative analyses used covariate-adjusted R-CHOP controls from the GOYA/BO21005 study, an appropriate contemporary benchmark for safety and efficacy. Safety and efficacy analyses included 206 patients. CR rate at EOT was 69% in the overall population and was maintained across Bcl-2 IHC-positive subgroups. With median follow-up of 32.2 months, trends were observed for improved investigator-assessed PFS for venetoclax plus R-CHOP in the overall population (Hazard ratio [HR] = 0.61, 95% confidence interval [CI], 0.43-0.87) and Bcl-2 IHC-positive subgroups (HR = 0.55, 95% CI, 0.34-0.89), versus R-CHOP. Despite a higher incidence of grade 3/4 hematologic adverse events (86%), related mortality was not increased (2%). Chemotherapy dose intensity was similar in CAVALLI versus GOYA. The addition of venetoclax to R-CHOP in 1L DLBCL demonstrates increased but manageable myelosuppression and the potential of improved efficacy particularly in high-risk, Bcl-2 IHC-positive patient subgroups.