The aim of this study was to develop an evidence-based psychosocial information booklet for parents of children without a specific diagnosis, many of whom are seen through the genetic clinic. A mixed methods approach was adopted involving four phases. The first two phases involving a systematic review and in-depth interviews are summarised briefly but reported in detail elsewhere. Phase 3 comprised: (1) a grey literature search to identify relevant literature and resources from other patient organizations; (2) drafting the booklet using themes identified through the previous phases; (3) piloting the booklet with eight professional and support group stakeholders and (4) piloting the booklet with 14 parents (from Phase 2) to ensure the information reflected their experiences. In Phase 4, we assessed satisfaction with the booklet through a questionnaire completed by 38 parents. The booklet was well accepted. The importance of providing the booklet at the beginning of the parental 'journey' was identified. We have developed an evidence-based information booklet to support parents via a rigorous mixed methods approach. This booklet meets a largely unmet psychosocial need and could be used in practice to support parents of children without a diagnosis.