OBJECTIVES:  Deaf BSL users can access standard Improving Access to Psychological Therapies (IAPT) services with interpreter assistance in the UK. Some areas use specialist IAPT services, adapted to meet cultural and linguistic needs of Deaf users, delivered by workers fluent in BSL. This NIHR HS&DR funded study (Ref: 12/136/79) assessed the cost-effectiveness of BSL-IAPT, compared to standard IAPT services, for Deaf BSL users. METHODS:  A combined decision tree (to capture the initial IAPT intervention period) and Markov model (to assess longer-term costs and health benefits) used a NHS and social care perspective to estimate the incremental cost/QALY and probability that BSL-IAPT is cost-effective. Data sources for clinical effectiveness, costs and utilities included systematic reviews, IAPT databases and new studies with Deaf BSL users. A 5 year timeframe was considered with costs and QALYs discounted. Probabilistic and deterministic sensitivity analyses assessed uncertainty. RESULTS:  If standard IAPT does not incur additional interpreter costs, then BSL-IAPT could be considered cost-effective if it achieves reliable recovery in 12% more cases than standard IAPT. If standard IAPT does incur additional interpreter costs, then BSL-IAPT is cost saving even if there is no difference in clinical efficacy. CONCLUSIONS:  This is the first economic evaluation of a healthcare intervention for Deaf BSL users and demonstrates services for Deaf people may be cost-effective. The costs of interpreters for standard IAPT and rate of recovery from depression are key cost-effectiveness drivers. This finding can support healthcare commissioners to achieve increased access to effective and efficient psychological therapies for depression.