OBJECTIVES:  To enable earlier access, licensing of new treatments is sometimes based on evidence from Phase II single-arm trials. For systematic reviews, there are many established filters for both randomized controlled trials (RCTs) and for observational studies of clinical evidence. This study aimed to determine if single-arm trials are being adequately captured by these filters given their increasing importance in re-imbursement processes. METHODS:  A targeted search of publically available filters for clinical evidence was performed with a focus on MEDLINE. Searches were subsequently carried out in Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Ovid MEDLINE(R) Daily and Ovid MEDLINE(R). Selected RCT and observational study filters were combined in turn and “single arm.ti,ab” studies not retrieved by these filter combinations were identified. From these trials, a list of commonly used free-text terms used in single-arm studies was compiled. These terms were evaluated to determine if they improved search sensitivity for such trials. RESULTS:  Targeted searches identified filters from several organisations including Cochrane, CADTH, BMJ, University of Texas School of Public Health and SIGN. All filters incorporated both MeSH terms and free-text terms. The combination of selected published RCT filters and observational study filters consistently failed to identify many single-arm trials; different filter combinations consistently missed the same studies. By reviewing a selection of abstracts of studies not captured by the published filters, a list of free-text terms commonly used to describe this trial design was compiled, including: single-arm, Phase II/Phase 2, prospective. Addition of a free-text line incorporating these terms to a search strategy improves search sensitivity for this trial design. CONCLUSIONS:  Current filters do not adequately capture single-arm trials. We identified additional free-text terms which could be used in conjunction with established filters to more comprehensively capture these trials.