OBJECTIVES: Linaclotide is a novel once daily, orally delivered peptide that acts on all key IBS-C symptoms. The aim of this analysis was to estimate the daily cost that would result in linaclotide being considered cost-effective in the UK, given different levels of willingness–to-pay (WTP). METHODS: A within-trial analysis was used to estimate the economically justifiable price from a payer perspective in the UK using patient-level data from a 26-week Phase III, randomized, double-blind trial of linaclotide 290µg daily (n=401) versus placebo (n=403) in IBS-C patients (modified Rome II criteria). EQ-5D data was collected at randomization and each subsequent visit. The UK valuation of the EQ-5D was applied to the raw data to estimate the utility for each patient.  Missing data were interpolated using the last-observation-carried-forward (LOCF) method. The WTP was varied from £15,000-£20,000/QALY. The only cost considered was that of linaclotide; total cost of treatment was weighted by compliance. Resource use was assumed to be equal between arms. Bootstrapping was performed to account for uncertainty. A scenario analysis was conducted using data from a 12-week linaclotide trial in a similar population. RESULTS: Patients treated with linaclotide gained 0.016 QALYs over the 26-week trial compared with patients in the placebo arm. At WTP thresholds of £15,000-£20,000/QALY linaclotide could be cost-effective at a price of £1.30-£1.70.  Over 75% of the bootstrap estimates fell below a willingness-to-pay threshold of £20,000/QALY. The method of addressing missing data had minimal impact on the ICER.  In the scenario analysis, the QALY gain for patients treated with linaclotide was even greater, thus a price of £2.00-£2.65 may result in linaclotide being considered cost-effective at thresholds of £15,000-£20,000/QALY. CONCLUSIONS: The base case analysis showed linaclotide could be cost-effective at a price of up to £1.70/day in the UK setting using conservative assumptions.