OBJECTIVE: To conduct a systematic review of studies on clinically relevant digital mobile phone electromagnetic interference with medical equipment. DATA SOURCES: MEDLINE and SUMSEARCH were searched for the period 1966-2004. The Cochrane Library and Database of Abstracts of Reviews of Effects were also searched for systematic reviews. STUDY SELECTION: Studies were eligible if published in a peer-reviewed journal in English, and if they included testing of digital mobile phones for clinically relevant interference with medical equipment used to monitor or treat patients, but not implantable medical devices. DATA SYNTHESIS: As there was considerable heterogeneity in medical equipment studied and the conduct of testing, results were summarised rather than subjected to meta-analysis. RESULTS: Clinically relevant electromagnetic interference (EMI) secondary to mobile phones potentially endangering patients occurred in 45 of 479 devices tested at 900 MHz and 14 of 457 devices tested at 1800 MHz. However, in the largest studies, the prevalence of clinically relevant EMI was low. Most clinically relevant EMI occurred when mobile phones were used within 1 m of medical equipment. CONCLUSIONS: Although testing was not standardised between studies and equipment tested was not identical, it is of concern that at least 4% of devices tested in any study were susceptible to clinically relevant EMI. All studies recommend some type of restriction of mobile phone use in hospitals, with use greater than 1 m from equipment and restrictions in clinical areas being the most common.