BACKGROUND: Mobile phone messaging, such as Short Message Service (SMS) and Multimedia Message Service (MMS), has rapidly grown into a mode of communication with a wide range of applications, including communicating the results from medical investigations to patients. Alternative modes of communication of results include face-to-face communication, postal messages, calls to landlines or mobile phones, through web-based health records and email. Possible advantages of mobile phone messaging include convenience to both patients and healthcare providers, reduced waiting times for health services and healthcare costs. OBJECTIVES: To assess the effects of mobile phone messaging for communicating results of medical investigations, on people's healthcare-seeking behaviour and health outcomes. Secondary objectives include assessment of participants' evaluation of the intervention, direct and indirect healthcare costs and possible risks and harms associated with the intervention. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2009, Issue 2), MEDLINE (OvidSP) (January 1993 to June 2009), EMBASE (OvidSP) (January 1993 to June 2009), PsycINFO (OvidSP) (January 1993 to June 2009), CINAHL (EbscoHOST) (January 1993 to June 2009), LILACS (January 1993 to June 2009) and African Health Anthology (January 1993 to June 2009). We also reviewed grey literature (including trial registers) and reference lists of articles. SELECTION CRITERIA: We included randomised controlled trials (RCTs), quasi-randomised controlled trials (QRCTs), controlled before-after (CBA) studies, or interrupted time series (ITS) studies with at least three time points before and after the intervention. We included studies assessing mobile phone messaging for communicating results of medical tests, between a healthcare provider or 'treatment buddy' and patient. We only included studies in which it was possible to assess the effects of mobile phone messaging independent of other technologies or interventions. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed all studies against the inclusion criteria, with any disagreements resolved by a third review author. Study design features, characteristics of target populations, interventions and controls, and results data were extracted by two review authors and confirmed by a third. Primary outcomes of interest were health outcomes and healthcare utilisation as a result of the intervention. We also considered patients' and providers' evaluation of the intervention, perceptions of safety, costs and potential harms or adverse effects of the intervention. MAIN RESULTS: We included one randomised controlled trial involving 2782 participants. The study investigated the effects of mobile phone messaging in alleviating anxiety in women waiting for prenatal biochemical screening results for Down syndrome, by providing fast reporting of results before a follow-up appointment. The study measured health outcomes using the Spielberger State-Trait Anxiety Inventory (STAI), which includes a scale (20 to 80 points, higher score indicates higher anxiety) to describe how the respondent feels at a particular moment in time (state anxiety). The study, which was at high risk of bias, found that women who had received their test result early by text message had a mean anxiety score 2.48 points lower than women who had not yet received their result (95% CI - 8.79 to 3.84). Women with a serum-negative test result receiving their result early had a mean anxiety score 5.3 points lower (95% CI - 5.99 to -4.61) than women in the control group. Women with a serum-positive test result receiving their result early by text message had a mean anxiety score 1.2 points higher (95% CI - 3.48 to 5.88) than women in the control group.The evidence was of low quality due to high risk of bias in the included study, and the fact that the evidence comes from one study only. The study did not report on other outcomes of interest, such as patient satisfaction, adverse events or cost. AUTHORS' CONCLUSIONS: We found very limited evidence of low quality that communicating results of medical investigations by mobile phone messaging may make little or no difference to women's anxiety overall or in women with positive test results, but may reduce anxiety in women with negative test results. However, with only one study included in this review, this evidence is insufficient to inform recommendations at this time. More research is needed on the effectiveness and user evaluation of these interventions. In particular, more research should be conducted into the potential risks and limitations of these interventions.