METHODS: A published model comprising a decision tree and a 3-state Markov model was adapted from a public payer perspective over a lifetime horizon. Adalimumab and secukinumab, having the highest market shares among biologics for the treatment of AS in Greece (standard practice) were selected as comparators in the analysis. Clinical parameters captured treatment response defined per ASAS20, short-term and long-term changes in Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Bath Ankylosing Spondylitis Functional Index (BASFI) scores long-term biologic treatment discontinuation, and adverse events. Efficacy, safety data and utility values were elicited from published literature. Direct costs pertaining to drug acquisition, monitoring, adverse events and disease management costs were considered in the analysis (€,2022). Model outcomes were patients’ quality-adjusted life years (QALY), total costs and incremental cost-effectiveness ratio (ICER).All future outcomes were discounted at 3.5% per annum.A probabilistic sensitivity analysis (PSA) was conducted to account for model uncertainty.