Aims/hypothesis. The aim of the work was to evaluate the vestibular organ condition in children and young adults suffering from Type I (insulin-dependent) diabetes mellitus. Methods. The group examined consisted of 95 children and young adults aged from 6 to 28 years with Type I diabetes diagnosed. The diabetic group was divided into subgroups according to duration of the disease, compensation of the disease, and presence and character of hypoglycaemic incidents, and presence of diabetic complications. The control group consisted of 44 healthy children and young adults aged 6 to 28 years. After collecting detailed medical history in each case an electronystagmographic test was performed using the computed two-canal electronystagmographer. Results. Within the diabetic group 6 patients complained about vertigo and balance disorders. Spontaneous nystagmus occurred in 10 cases, positional one in 21 cases. Impaired optokinesis occurred in 36 cases and impaired eye tracking test in 33 cases. In caloric tests there was partial canal paresis in 4 cases and directional preponderance in 7 cases. Conclusion/interpretation. Metabolic disturbances present in Type I diabetes cause disturbances in different parts of vestibular organ but mostly in its central part. Comparing disturbances in the vestibular organ with clinical and biochemical parameters characterising diabetes, the range of vestibular organ impairment in diabetes mellitus type 1 seems to depend mainly on the presence and character of hypoglycaemic incidents and the duration of the disease and to some extent on the compensation of diabetes. [Diabetologia (2002) 45:728-734]