The aims of this study were to review what is currently known about comorbidity in people with Down's syndrome and to determine if their relative risk for certain disorders was increased. Analysis was carried out on the published literature from 1982 through 1994. In order to be included in this study, articles had to meet predetermined criteria. The strengths and weaknesses of the selected articles were considered in this review. The estimation of relative risks was done by calculating the odds ratio (OR). Odds ratios of > 2 or < 0.5 were found in more than one article for congenital heart defects, hypothyroidism, hearing impairment and hepatitis B. Only one article indicated an OR within this range for all of the following disorders: obesity, epilepsy, degenerative spine disorders and a wide atlanto-axial distance. The results were unclear in the areas of hyperthyroidism, visual disorders, dementia and psychiatric disorders. The concept of comorbidity, i.e. establishing the relationships between the various conditions in one person and understanding the implications for medical care, seems promising, especially for people with intellectual disability. Further work in this area may well improve the quality of care offered to these people.