Multimorbidity, defined as having two or more chronic health conditions, is associated with elevated polypharmacy and mortality. Autism spectrum disorder is a whole-body chronic health condition in which comorbidities -- in particular co-occurring intellectual disability -- contribute to high clinical heterogeneity, polypharmacy and premature mortality. We aimed to determine specific multimorbidity patterns among autism spectrum disorder + intellectual disability adults, and to identify participants' subgroups based on multimorbidity features. We used baseline examination data from a previous exploratory prospective multicentric study that included 63 autism spectrum disorder + intellectual disability adults. Multimorbidity patterns and subgroups were determined using clustering approaches. We observed 84.1% multimorbidity, significantly associated with age. We identified a dominant multimorbidity pattern, combining immune dysfunction, gastrointestinal disorders, neurological, and joint diseases. Four participants' subgroups could be distinguished by multimorbidity, autonomy and polypharmacy. Two clusters were distinguished by the prevalence and consequences of multimorbidity. One cluster involved women with endocrine disorders. The final cluster was composed of older adults with the lowest autism spectrum disorder severity but greater multimorbidity, including cardiovascular and kidney diseases. Our results support a role for the gut-brain axis in the pathophysiology of autism spectrum disorder + intellectual disability multimorbidity. Furthermore, we identified patient subgroups with specific needs, underscoring the importance of a holistic approach for autism spectrum disorder + intellectual disability adults.