This paper presents a summary of the evidence review group (ERG) report into the clinical effectiveness and cost-effectiveness of eltrombopag for the treatment of adults with chronic idiopathic (immune) thrombocytopenic purpura (ITP), based on a review of the manufacturer’s submission (MS) to the National Institute for Health and Clinical Excellence (NICE) as part of the single technology appraisal process. ITP is an autoimmune disorder by which antibodies are formed against platelets with annual incidence rates in the UK/USA ranging from 1.13 to 6.62 cases per 100,000 adults. Eltrombopag increases the production of platelets at a rate that outpaces their destruction by the immune system, and has a UK marketing authorisation both for the treatment of adult ITP in splenectomised patients who are refractory to other treatments and as a second-line treatment for adult non-splenectomised patients for whom surgery is contraindicated. Both splenectomised and non-splenectomised patient groups were considered in the analysis. Two economic models were presented, one for a watch-and-rescue treatment scenario and the second for the long-term treatment of patients with more severe ITP. The submission’s evidence was sourced from the relatively high-quality RAISE [RAndomized placebo-controlled Idiopathic thrombocytopenic purpura (ITP) Study with Eltrombopag] randomised controlled trial. The study indicated a statistically significant difference in favour of eltrombopag compared with placebo in the odds of achieving the primary outcome of a platelet count of between 50 and 400 × 109/l during the 6-month treatment period (odds ratio 8.2, 99% confidence interval 3.6 to 18.7). In the eltrombopag group, 50/83 (60%) non-splenectomised patients and 18/49 (37%) splenectomised patients achieved this outcome. Median duration of response for all patients was 10.9 weeks (splenectomised patients 6 weeks and non-splenectomised patients 13.4 weeks). Patients treated with eltrombopag required less rescue medication and had lower odds of bleeding events than placebo-treated subjects in both patient groups. In the watch-and-rescue economic model, the ERG found that substantial reductions in the cost of eltrombopag are needed for the incremental cost-effectiveness ratio (ICER) to fall below £30,000. Further analyses found that the ICER varied from £33,561 to £103,500 per quality-adjusted life-year (QALY) (splenectomised) and from £39,657 to £150,245 per QALY (non-splenectomised). Other than bleeding, no adverse events were modelled. In relation to the long-term treatment model, the ERG found that using non-randomised non-comparative data may result in biased estimates of unknown magnitude and direction. None of the treatment sequences resulted in an ICER approaching the recommended threshold of £30,000. The base-case results, using a 2-year time horizon and prescribing eltrombopag as second-line treatment post rituximab, were found to be favourable towards eltrombopag. In conclusion, based on the MS and additional ERG work, eltrombopag appears to be a safe treatment for ITP (although long-term follow-up studies are awaited) and has short-term efficacy. However, there is no robust evidence on long-term efficacy or cost-effectiveness of eltrombopag, and there is a lack of robust direct evidence on the effectiveness and cost-effectiveness of eltrombopag compared with other relevant comparators. NICE did not recommend eltrombopag for the treatment of chronic ITP within its marketing authorisation for splenectomised or non-splenectomised patients.