Objectives: We evaluated the cost-effectiveness of rituximab added to the chemotherapy regimen of fludarabine plus cyclophosphamide (R-FC) versus fludarabine plus cyclophosphamide (FC) for the treatment of patients with previously untreated or relapsed/refractory chronic lymphocytic leukemia (CLL). Methods: Two Markov models were built, using published results on progression-free survival (PFS) in patients receiving first- or second-line therapy with R-FC vs FC, rates of disease progression and mortality rates in Spain. Patient-elicited utilities were applied to PFS and progressed health states. The cost of drugs, supportive care, and quality-adjusted life years (QALY) were estimated over a 10-year period. Univariate and probabilistic (Monte Carlo) sensitivity analyses were performed. Results: The addition of rituximab to chemotherapy in first- and second-line therapy increased life-years gained (LYG) and QALYs compared with chemotherapy. The incremental cost per LYG and QALY gained was €20,703 and €19,343 for first-line treatment and was €23,183 and €24,781 for second-line treatment. Conclusion: In patients with previously untreated or relapsed/refractory CLL, the addition of rituximab to the FC regimen increased life expectancy and quality-adjusted life expectancy. In both types of patient, the treatment was cost-effective.