This paper presents a summary of the evidence review group (ERG) report into the clinical effectiveness and cost-effectiveness of azacitidine (aza) compared with conventional care regimes (CCR) for higher risk patients with myelodysplastic syndrome (MDS), chronic myelomonocytic leukaemia (CMML) and acute myeloid leukaemia (AML), based on the evidence submission from the manufacturer to the National Institute for Health and Clinical Excellence (NICE) as part of the single technology appraisal process. The patient outcomes governing relative effectiveness and cost-effectiveness were defined as overall survival, time to progression (TTP) to AML, adverse events and health-related quality of life (HRQoL). The clinical evidence was derived from an open-label randomised controlled trial referred to as study AZA-001. It compared aza with CCR in 358 patients with higher risk MDS, CMML and AML 20-30% blasts. The outcomes reported in AZA-001 included overall survival, TTP to AML and adverse events. No HRQoL results were reported; however, outcomes likely to impact on HRQoL were provided. The results showed that: the median overall survival was 24.5 months on aza, compared with 15.0 months in the CCR group = 0.0001); the response rates were low (complete remission 17% aza versus 8% CCR); the median time to transformation to AML was greater in the aza group (17.8 versus 11.5 months; p <0.0001); and of patients who were red blood cell (RBC) transfusion-dependent at baseline, 45% of those on aza became RBC transfusion-independent during the treatment period, compared with 11.8% in the CCR group (p <0.0001). The ERG reran the submission's search strategies after some modifications incorporating minor improvements. The ERG analysed the submitted economic model (model 1) and identified a number of inconsistencies and errors within the model. The manufacturer submitted a revised model for analysis by the ERG. Using the issues identified in the earlier analysis, the ERG conducted those repairs to the revised model that were feasible within time constraints. The ERG ran this version in probabilistic sensitivity analyses to generate cost-effectiveness acceptability frontiers. The results of these exploratory analyses indicated that: for standard-dose chemotherapy (SDC)-treated patients, of six treatment options available, best supportive care (BSC) was likely the most cost-effective option up to a threshold of (sin)51,000/quality-adjusted life-year (QALY) [beyond (sin)51,000/QALY, aza + low-dose chemotherapy (LDC) became cost-effective]; for LDC-treated patients, of four options available, BSC was again the most cost-effective option up to a willingness-to-pay threshold of (sin)51,000/QALY (aza + LDC became cost-effective after (sin)51,000/QALY); for BSC-treated patients, aza + BSC became cost-effective relative to BSC at a threshold of about (sin)52,000/QALY. The ERG considers these results exploratory and considers that they should be viewed with caution. The AZA-001 study showed that, compared with CCR, those MDS patients receiving aza had prolonged median survival, had delayed progression to AML, had reduced dependence on transfusions and had a small improvement in response rate. Given the general paucity of economic modelling work in MDS and the limitations of the submitted industry model there is an evident need for an independent cost-effectiveness analysis of aza in MDS. At the time of writing, the guidance appraisal consultation document issued by NICE on 4 March 2010 states that azacitidine is not recommended as a treatment option for people no eligible for haemopoietic stem cell transplantation with the the following conditions: intermediate-2 and high-risk MDS according to the International Prognostic Scoring System, CMML with 10-29% marrow blasts without myeloproliferative disorder, or with AML with 20-30% blasts and multilineage dysplasia, according to World Health Organization classification.