Ownership of personal digital assistants (PDAs) and smartphones by health professionals is increasingly common. Providing the best available evidence at the point of care is important for time-poor clinical staff and may lead to benefits in the processes and outcomes of clinical care. This review was performed to investigate the usefulness of PDAs in the clinical setting. MEDLINE, Embase, CINAHL and the Cochrane Central Register of Controlled Trials were searched from 2000 to March 2010. Randomised controlled trials that evaluated the effects on the processes or outcomes of clinical care of using PDAs compared with not using a PDA were included. Two reviewers independently reviewed citations and abstracts, assessed full text articles and abstracted data from the studies. Seven trials met the review inclusion criteria, of which only three were of satisfactory quality. Studies investigated the use of PDAs either in recording patient information or in decision support for diagnoses or treatment. An increase in data collection quality was reported, and the appropriateness of diagnosis and treatment decisions was improved. PDAs appear to have potential in improving some processes and outcomes of clinical care, but the evidence is limited and reliable conclusions on whether they help, in what circumstances and how they should be used are not possible. Further research is required to assess their value and ensure full benefits from their widespread use, but the pace of technological development creates problems for the timely evaluation of these devices and their applications.