Advances in immunological and genetic tests and in therapeutics may soon make it possible to predict, prevent or delay the development of type 1 diabetes mellitus (DM). Psychological support should be available at every stage of the screening and prevention process for high-risk individuals. Each step in this process results in a threat to the affected individual and his/her family, followed by anxiety, decision processes, uncertainty, conflicts and depression, and also attempts to cope with these. At the first step, information about the screening procedure is provided, and an attempt is made to motivate individuals and families to take part. At the second step, there is notification of risk and, for the small group of marker-positive individuals, an invitation to participate in a prevention trial. At the third step, the individuals included in a prevention protocol have to deal with anxiety over receiving placebo, maintain cooperation with therapy, and cope with potential failures of the prevention. There are only a few psychological data gained in DM screening or intervention studies, showing high clinical anxiety while screening, both before and after notification of risk. After a few months of anxiety, it usually drops to normal levels, but family functioning seems to be changed. Data are explained within the framework of an extended Health Belief Model. Data regarding the psychological impact on family members and identification of variables related to continued study participation are needed for studies seeking to recruit and retain subjects in longitudinal protocols for prediction and prevention of type 1 DM.