OBJECTIVES: There are few treatments available for advanced melanoma and survival rates are low. While the incidence of the disease continues to rise, only two new treatments have come to the market recently: ipilimumab and vemurafenib. Ipilimumab is indicated in Europe for the treatment of advanced melanoma in adults who have received prior therapy. Ipilimumab has demonstrated a statistically significant improvement in overall survival in 2 Phase III RCTs. Prolonged survival (>2 years in some patients) has been shown (MDX020 & 024). METHODS: Data from the MDX010-20 trial, which was conducted in previously treated patients with a maximum follow up duration of 55 months, was used to develop an economic model for health technology assessment in England & Wales. This model has been used to predict the conditional survival (CS) of patients treated with ipilimumab (based on both ipilimumab containing arms) compared to gp100 – the active control. The model used patient level Kaplan–Meier data for the first 18 months, parametric curves fitted to the patient level data from 18 months to 5 years, and published AJCC registry data beyond 5 years.  RESULTS: The curves were a good fit to the MDX010-20 trial data (MAE 0.003) and consistent with published Phase II data (which provides a longer time horizon). Given an ipilimumab patient has survived 2 years, the modelled probability of being alive at 5 years is 67% (49%,79%)  (gp100: 15%  [9%,21%])  and at 10 years is 54% (39%, 63%) (gp100: 2%  [1%,3%]).  CONCLUSIONS: The model shows that a substantial proportion of patients treated with ipilimumab surviving to 2 years are likely to have sustained survival benefits: more than 50% of ipilimumab patients surviving to 2 years are alive at 10 years, with 29% remaining alive at 20 years. This level of sustained survival is not shown by gp100 patients.