BACKGROUND: Single-arm trial (SAT) data is increasingly reviewed for drug approvals by regulators and Health Technology Assessment (HTA) bodies. Supplementary data in the form of external comparators (ECs) can be used to provide clinical context to support these drug evaluations. In this study we characterized HTAs for SAT-based submissions, the use of supplementary EC data and outcomes from HTA review. METHODS: HTA Accelerator database was used to describe SAT-based HTA submissions with decisions (2011-2019). RESULTS: A total of 433 SAT-based HTA submissions were identified between 2011 and 2019 with a 13-fold increase during this period. Around 65%(283/433) were in oncology or hem-oncology. Around 52%(226/433) of submissions contained some type of EC data, including prior clinical trials (24%, 104) and real-world data (RWD) (20%, 87), but 40%(175) contained no EC data. The overall acceptance rate for SAT-based submissions was 48% and with RWD EC data acceptance was 59%. In the latest 5-year period (2015-2019), use of RWD ECs increased 22% as a proportion of submissions per year, whereas, prior trial ECs decreased (-14%) and use of no EC remained stable (-2%). Between 2015 to 2017 and 2018 to 2019, acceptance rate for RWD ECs increased by 20% (41% in 2015-2017 to 61% in 2018-2019) whereas prior trial EC use decreased by 10% and no EC submissions decreased 16%. Of 226 submissions using ECs, only 29%(66) used an adjusted indirect treatment comparison method. CONCLUSIONS: SAT-based submissions to HTA bodies are rapidly evolving in terms of composition and acceptance. Types of EC and methodological approach used are important determinants of positive outcomes.