Background  Individuals with Down syndrome increasingly survive into adulthood, yet little is known about their healthcare patterns as adults. Our study sought to characterise patterns of health care among adults with Down syndrome based on whether they had fully transitioned to adult‐oriented providers by their inception in this cohort.Methods  In this retrospective observational cohort study, healthcare utilisation and annualised patient charges were evaluated in patients with Down syndrome aged 18–45 years who received care in a single academic health centre from 2000 to 2008. Comparisons were made based on patients' provider mix (only adult‐focused or ‘mixed’ child‐ and adult‐focused providers).Results  The cohort included 205 patients with median index age = 28 years; 52% of these adult patients had incompletely transitioned to adult providers and received components of their care from child‐focused providers. A higher proportion of these ‘mixed’ patients were seen exclusively by subspecialty providers (mixed = 81%, adult = 46%, P < 0.001), suggesting a need for higher intensity specialised services. Patients in the mixed provider group incurred higher annualised charges in analyses adjusted for age, mortality, total annualised encounters, and number of subspecialty disciplines accessed. These differences were most pronounced when stratified by whether patients were hospitalised during the study period (e.g. difference in adjusted means between mixed versus adult provider groups: $571 without hospitalisation, $19 061 with hospitalisation).Conclusions  In this unique longitudinal cohort of over 200 adults aged 18–45 years with Down syndrome, over half demonstrated incomplete transition to adult care. Persistent use of child‐focused care, often with a subspecialty emphasis, has implications for healthcare charges. Future studies must identify reasons for distinct care patterns, examine their relationship with clinical outcomes, and evaluate which provider types deliver the highest quality care for adults with Down syndrome and a wide variety of comorbidities.