Mental disorders and physical health problems are common among adults with intellectual disabilities, as they accompanied with mental disorders are always present higher levels of functional disability than those with intellectual disabilities only. This review aims to describe the characteristics and the impacts of older people with intellectual disabilities accompanied with mental disorders in their daily livings. Results reveal that the prevalence of MD is high in adults of all ages with ID; there was no significant difference in older people with ID and younger people with ID. Individuals with ID attending psychiatric services were more likely to be older and polypharmacy was commonplace for older adults with ID. Higher family impact was also found between caregivers to adults with intellectual disabilities and mental disorders. This review highlights that adults with intellectual disabilities have higher mental disorder service needs which require recognition and the allocation of specific resources to protect the same right to healthy ageing as their counterparts living without ID. Further research is needed to improve our understanding of the adverse effects of ageing on the mental disorders and care needs of older people with intellectual disabilities.