Objectives: This study used the grounded theory to explore parents' views of the transition into adulthood of their child with a severe intellectual disability. The study also sought to explore the processes that parents engage in for making psychological adjustments, to appreciate their role during this transition. This study is imperative for developing a psychologically informed theory that can be understood by both parents and clinicians. Methods: Twelve parents of 11 children with a severe intellectual disability were recruited for interview from charitable organizations accessed by parents (e.g. Mencap). Data collection used a combination of open-ended structured questions and non-directed probing. NVivo 10 software was used to assist the grounded theory coding and analysis process. Results: The analysis developed five processes that parents engaged in during their child's transition into adulthood: 'defining adulthood', 'noticing adult development', 'perceiving barriers to adulthood', 'worrying,' and 'making psychological adjustments'. Common to these was seen to be a core process of 'making comparisons with perceived "norms"'. Contrasting findings are critically discussed alongside extant literature. Additionally, a transition model of parents' views and adjustments is proposed, grounded in the study findings. Conclusions: Parents engage in a series of interactional processes throughout the transition trajectory, which are likely to influence how they make adjustments. Clinical interventions could challenge parent perceptions; encourage peer support; embrace systemic ways of working with parents through their child's transition into adulthood; and use the presented model to help parents understand their experiences and any adjustment-related problems.