OBJECTIVES: Chronic Lymphocytic Leukaemia (CLL) is an indolent progressive hematologic disease. Current treatments for CLL are not curative and subjects become increasingly resistant to subsequent therapies. Patients relapsing after a disease-free period shorter than 2 years have an anticipated overall survival of 45% at 3 years. Idelalisib + rituximab is improving overall and progression-free survival compared to rituximab + placebo in early (<2 years) relapsed CLL patients. This trial was stopped early because of overwhelming efficacy. We estimated the cost-effectiveness of Idelalisib + rituximab in the French context.  METHODS: A partitioned survival model was used to compare Idelalisib + rituximab to currently available treatments in France: alemtuzumab, bendamustine-rituximab and ibrutinib for CLL patients with early relapse and fludarabine-cyclophosphamide-rituximab, bendamustine-rituximab and ibrutinib for CLL patients with late relapse. Because of the lack of an identifiable trial network and the presence of single arm trials, we used an innovative approach for comparing survivals. In essence, the modelling was based on fitting a general survival parametric function for all treatments, and then adjusting the scale parameters of the function to fit the observed survivals in each study (i.e.”common gamma approach”). Time horizon was 10 years. Utilities associated with different stages of disease were based on data from the literature. French direct medical costs were used. Outcomes and costs were discounted at 4%. Price for idelalisib was the price used in the early access program in France.  RESULTS: Idelalisib + rituximab was associated with incremental cost-effectiveness ratios of 30 480 €/QALY in early relapse and 31 312 €/QALY in late relapse. Sensitivity analyses showed that the result was highly sensitive to the efficacy of idelalisib partly explained by the immaturity of the survival data coming from a clinical study with early termination. CONCLUSIONS: Idelalisib is a cost-effective option for the treatment of early and late relapse CLL patients.