Building on the prior work of use of pentostatin in chronic lymphocytic leukemia (CLL), we initiated a trial of combined pentostatin (2 mg/m2), cyclophosphamide (600 mg/m2), and rituximab (375 mg/m2) for 65 symptomatic, previously untreated patients. Of 64 evaluable patients, 34 (53%) were high Rai risk, 71% were nonmutated for the immunoglobulin heavy-chain variable region gene, 34% were CD38+, and 34% were ZAP-70+. Thirty patients (52%) had one anomaly detected by fluorescence in situ (FISH) hybridization, and 21 (36%) had complex FISH defects. Thirty-eight patients (58%) had grade 3+ hematologic toxicity but minimal transfusion needs and no major infections. Responses occurred in 58 patients (91%), with 26 (41%) complete responses (CRs), 14 (22%) nodular partial responses (nodular PRs), and 18 (28%) partial responses (PRs). Many patients with a CR also lacked evidence of minimal residual disease by 2-color flow cytometry. Examination of prognostic factors demonstrated poor response in the 3 patients with del(17p). In contrast, we found this regimen was equally effective in young versus older (>70 years) patients and in del(11q22.3) versus other favorable prognostic factors. Thus, this novel regimen of pentostatin, cyclophosphamide, and rituximab for previously untreated patients with CLL demonstrated significant clinical activity despite poor risk-based prognoses, achievement of minimal residual disease in some, and modest toxicity.