Objective: The terms used to refer to people who receive mental healthcare have been described as either potentially stigmatizing or empowering. This paper systematically reviews empirical studies of terminological usage in order to ascertain current knowledge.Methods: Multiple databases were searched using the terms 'patient', 'client', 'service user' and 'consumer'. Empirical, English language studies were included where an aim was to measure outcome related to the various terms used to describe or refer to people who use mental health services. Studies were assessed (i) against a hierarchy of evidence and (ii) using a 12-item checklist of methodological quality.Results: The search resulted in the screening of 13,765 abstracts; full text versions of 69 papers were examined and 11 studies that met the inclusion criteria were identified. All were cross-sectional surveys and all measured participant preference. Nine studies satisfied four or fewer quality markers. 'Client' and 'patient' were the terms preferred by study participants.Conclusions: Despite a stream of debate in editorial columns and letters pages, it is unclear whether terminological use is important to the people who use mental health services. Preference is the sole outcome investigated empirically. Methodological rigour of extant study findings is largely questionable. Generalization and interpretation from included studies should be approached very cautiously.