OBJECTIVES : Spinal muscular atrophy type I (SMA-I) is a rare genetic condition usually diagnosed before 6 months of age. Health utilities are required to evaluate the economic impact of treatments for SMA-I. However, it is impossible for these to be derived directly from affected children. The aim of this study was to derive SMA-I health utilities via vignettes. METHODS : Participants were presented with 4 vignettes describing SMA-I health states that differed in levels of severity: 1. Permanent Assisted Ventilation (PAV); 2. Non-sitting; 3. Sitting; and 4. Walking. Participants were asked to imagine themselves as parents to a child with SMA. For each vignette participants first determined whether the state was worse than death (WTD) using a visual analogue scale (VAS) (range: -100 to 100). Health state utilities were then captured using time trade-off (TTO) and standard gamble (SG). Task wording was varied depending on whether the state was rated WTD. The study was completed online with a representative sample of the UK adult population. RESULTS : 321 participants completed the study (age: 18-65; 49.7% females). Mean health state utilities for TTO were: -0.0243 [PAV, 95% confidence interval: -0.0914, 0.0428]; -0.0264 [Non-sitting, -0.0966, 0.0438]; 0.0977 [Sitting, 0.0291, 0.1664]; 0.3844 [Walking, 0.3225, 0.4463]. For the SG: 0.0028 [-0.0611, 0.0677], 0.0139 [-0.0505, 0.0783], 0.0946 [0.0302, 0.1591] and 0.3782 [0.3176, 0.4388]. The least severe health state (“Walking”) differed significantly from the other three states (p<0.0001). Mean utilities were not statistically significant for the worst 2 health states. CONCLUSIONS : Mean health state utilities differed in line with severity of SMA-I. Although participants were not able to discriminate between the two worst health states, this, and the relatively low spread between mean utilities reflect the severity of SMA. These results contribute to a growing body of utility data for use in economic models of SMA treatments.