Background Recent advances in genetics are particularly relevant in the field of intellectual disability (ID), where sub-microscopic deletions or duplications of genetic material are increasingly implicated as known or suspected causal factors. Data-driven reports on the impact of providing an aetiological explanation in ID are needed to help justify widespread use of new and expensive genetic technologies. Methods We conducted a survey of caregivers on the value of a genetic/aetiologic diagnosis of 22q11.2 deletion syndrome (22q11.2DS), the most common microdeletion syndrome in ID. We also surveyed the opinion of a high-functioning subset of adults with 22q11.2DS themselves. We used standard quantitative and qualitative methods to analyse the responses. Results In total, 73 of 118 surveys were returned (61.9%). There was convergence of quantitative and qualitative results, and consistency between adult patient and caregiver responses. A definitive molecular diagnosis of 22q11.2DS was a critical event with diverse positive repercussions, even if occurring later in life. Frequently cited benefits included greater understanding and certainty, newfound sense of purpose and a platform for advocacy, and increased opportunities to optimise medical, social and educational needs. Conclusions This is the first study to characterise the impact of a diagnosis of this representative microdeletion syndrome on adult patients and their families. The results both validate and expand on the theoretical benefits proposed by clinicians and researchers. The use of genome-wide microarray technologies will provide an increasing number of molecular diagnoses. The importance of a diagnosis of 22q11.2DS demonstrated here therefore has implications for changing attitudes about molecular genetic diagnosis that could benefit individuals with ID of currently unknown cause and their families. [ABSTRACT FROM AUTHOR]