Advances in genomic medicine have lead to debate about the potential inclusion of genetic tests for susceptibility to common complex disorders in newborn screening programmes. Empirical evidence concerning psychosocial reactions to genetic testing is a crucial component of both ethical debate and policy development, but while there has been much speculation concerning the possible psychosocial impact of screening newborns for genetic susceptibilities, there remains a paucity of data. The aim of the study reported here is to provide some of this missing empirical evidence, using type 1 diabetes as an example of a common disorder with multiple significant genetic contributors to its aetiology. Semi-structured interviews were conducted with 11 parents of babies who had received increased risk results in a study that involved newborn screening for genetic susceptibility to type 1 diabetes. Interpretative phenomenological analysis was used to evaluate the data. The interview data suggest that the probabilistic nature of results of genetic susceptibility tests impacts upon all aspects of parents' psychosocial reactions, resulting in a complex and dynamic process quite different to that described in relation to current newborn screening programmes. While parents generally reported fairly minor levels of concern in response to news of their child's increased genetic risk, these worries frequently recurred, and perception of risk also varied and fluctuated over time. Both individual and contextual factors appeared to interact with the inherent uncertainty of the test result to contribute to the dynamic nature of parental reactions, and their behavioural responses. The implications of these findings for future research and for the debate concerning potential expansion of newborn screening are discussed.