Children with Down's syndrome have an increased risk of congenital anomalies and additional medical problems. These can be treated but are often seen as part of the syndrome and not as the cause of developmental retardation. Based on the current level of knowledge, specific medical tests and evaluations are recommended. The reasons for these guidelines, composed by the Down's syndrome Work Group of the Paediatric Association of the Netherlands, are illustrated by the case reports of five patients: in a 4-year-old boy, retardation improved after celiac disease had been diagnosed. In a 5-year-old boy, slow speech development was reversed after hearing loss was diagnosed. In a 2-year-old girl, development improved after a mitral valve stenosis had been corrected. In a 6-month-old boy, drinking problems were reversed when torticollis was diagnosed and a self-deflating drinking bottle was introduced. An adult man suffering from epilepsy and from self-mutilative rubbing and hitting of his eyes, regained his sight after cataract, myopia and atrophy bulbi were diagnosed. A well-balanced disclosure of the diagnosis, repeated medical screening, early motor training and social interventions combined with active parental participation, warrant optimal development. In cooperation with the Down's syndrome Parent Association, multidisciplinary medical teams have been established to offer and promote this care.