In this mixed methods study, a survey and in-depth interviews were used to explore whether decision regret and the psychological impact of receiving genome sequencing (GS) results differed between parents and patients, and between those who received a genetic diagnosis and those who did not. Participants (n = 77) completed a survey that included the Decisional Regret Scale (DRS) and an adaptation of the Multidimensional Impact of Cancer Risk Assessment (MICRA) at least 12 months after consenting for GS for rare disease diagnosis in the 100,000 Genomes Project. Survey participants were invited to take part in an interview and 39 agreed; 12 with a diagnosis, 5 with variants of uncertain significance, and 19 with no pathogenic findings identified. Both survey and interview findings indicated that decision regret was low. DRS scores revealed no differences in levels of regret between parents and patients, or between those with a diagnosis and those without. Though MICRA scores indicated minimal evidence of negative psychological impacts of receiving GS results, subscale analysis revealed greater distress and uncertainty for parents compared to patients. Receiving a diagnosis was found not to influence MICRA scores, supporting interview findings of both positive and negative emotional and psychological impacts irrespective of a genetic diagnosis. Our findings have implications for policy and practice as GS is integrated into the UK and worldwide; notably, that expectation-setting is critical when offering GS, and that post-test counselling is important regardless of the GS result received, with parents perhaps needing additional emotional support.