Background Down syndrome (DS) is the most frequent chromosomal condition; however, knowledge about associated health issues in adulthood is inadequate. We aimed to obtain health information from Japanese adults with DS.

Methods We conducted a retrospective chart review of 151 patients with DS who visited the Internal Medicine Outpatient Department of the Tokyo Metropolitan Kita Medical and Rehabilitation Center for the Disabled.

Results Endocrine disorders, such as obesity, hyperlipidemia, and hyperuricemia, were most common in both adulthood (≤ 40 years) and senescence (> 40 years), whereas neurological diseases were more prevalent in senescence. Even patients with DS in their 20s or younger had multimorbidity that increased with age. Only 21 patients (13.9%) with DS visited our hospital with referral letters from pediatricians; 94 patients (62.3%) visited without referral letters from other medical institutions. Patients without a referral letter had a mean of 3.1 comorbidities per patient. Moreover, medical care for people with DS was interrupted during childhood in some cases.

Conclusions From our results, to prevent and detect comorbidities in patients with DS, there is need for continuous medical care from childhood to adulthood. Recently, individuals with DS have been diagnosed using chromosome testing and genetic counseling. Clinical geneticists and genetic counselors can support patients with DS and their caregivers in achieving appropriate health care and well-being on their own by seamlessly engaging them throughout childhood and adulthood.