BACKGROUND The prevalence of chronic lymphocytic leukemia (CLL) increases with age. Although chemoimmunotherapy (CIT) has dramatically improved response rates in patients with CLL, some CIT regimens are not well tolerated by many patients >or=70 years of age. METHODS Sixty-four previously untreated patients with CLL and serum creatinine <1.5 times the upper limit of normal who met National Cancer Institute (NCI) 96-WG criteria for treatment received pentostatin (2 mg/m(2)), cyclophosphamide (600 mg/m(2)), and rituximab (375 mg/m(2)). The authors measured performance status at study entry and used age, weight, and baseline creatinine to calculate creatinine clearance (CrCl). RESULTS Eighteen of 64 (28%) patients were ages >or=70 years. Although individuals ages >or=70 years were more likely to have delayed treatment cycles (28% vs 7%; P=.03), there were no significant differences in the number of cycles administered, need for dose reductions, or grade 3-4 hematologic, infectious, or other toxicities. No significant differences in overall response rate, complete response rate, or progression-free survival were observed by age. Twenty-five (39%) patients had a CrCl < 70 mL/min (range, 34-67). Although individuals with CrCl < 70 were more likely to require dose reduction (24% vs 5%; P=.05), there were no significant differences in the number of cycles administered or grade 3-4 hematologic, infectious, or other toxicities. No significant difference in overall response rate, complete response rate, or progression-free survival were observed between patients with CrCl >or= 70 mL/min and those with CrCl < 70 mL/min. CONCLUSIONS In this clinical trial, the PCR regimen was well tolerated by older patients and individuals with CrCl <or= 70. The efficacy of PCR was not significantly affected by age or renal function. These findings suggest PCR may be a good therapeutic option for older patients and those with modestly decreased renal function.