The aim of this review is to determine the frequency and circumstances under which predicting individuals' risk of illness has adverse psychological effects. Using systematic review methodology, the literature was searched for studies that had assessed the adverse psychological outcomes of risk assessment programmes. The outcomes investigated are emotional (anxiety, depression, distress) cognitive (intrusive thoughts, perceptions of health) and behaviour (work absenteeism). The impact of both positive and negative test results are summarised in terms of the number of studies showing significant effects between and within groups in the short (one month or less) and longer term (more than one month). Where sufficient data were available, a meta-analysis was conducted to assess effect size. Fifty-four studies met the criteria for inclusion. The studies assessed the impact of informing individuals about cardiovascular risk (21), risk of AIDS (eight), risk of cancer (10), risk of Huntington's disease (10), risk of diabetes (two), risk of spinocerebellar ataxia (one) and risk of osteoporosis (two). Overall, the quality of studies assessed was limited, with only two using a randomised design to determine the psychological impact of risk assessment. Receiving a positive test result was associated in the short term in the great majority of studies with depression, anxiety, poorer perceptions of health and psychological distress. Data were available for a quantitative synthesis of results on three outcomes, anxiety, depression and distress. Anxiety and depression were significantly higher in those tested positive compared with those tested negative in the short term but not the longer term. Distress could only be assessed in the longer term: there was no evidence of an increase for those receiving positive test results. The five experimental studies that reported interventions aimed at preventing some of these adverse effects all reported favourable results. There was little evidence of any adverse psychological effects of receiving an unfavourable test result. Adverse psychological effects are a common immediate consequence of positive test results following risk assessment. Results from the few experimental studies reviewed suggest that these adverse outcomes should not be seen as inevitable.