It is commonly known that there is a higher risk of diabetes type 1 in relatives of patients with diabetes type 1. According to some reports in families of these patients the incidence of diabetes type 2 is also higher. The aim of our study was the evaluation of incidence of diabetes type 1 and 2 in 1st and 2nd degree relatives of patients with diabetes type 1. Our study was conducted in the years 1993-2000 in the Department of Endocrinology for Children and Adolescents in Wrocław and in the Department of Endocrinology of Jagiellonian University in Cracow among relatives of all the patients in the age of 0-19 years with newly diagnosed diabetes type 1. Special prepared questionnaires were used in which patients were asked about: number of relatives of 1st and 2nd degree, age, sex and diagnosis of diabetes in the relatives. Data from families of 332 patients were obtained. They concerned 4080 relatives. Diabetes occurred in 121 relatives (2.96%). 20 of them were 1st degree relatives and 101--2nd degree relatives. In 31 relatives (0.76%) diabetes type 1 was diagnosed and in 88 relatives (2.16%) diabetes type 2 was diagnosed. Except for one individual (patient's mother) diabetes type 2 occurred in 2nd degree relatives. Diabetes type 1 was diagnosed in 16 1st degree relatives and 15 2nd degree relatives. They were: 1st degree relatives: 9 fathers, 3 brothers, 2 mothers and 2 sisters. 2nd degree relatives: in 8 cases siblings of patient's parents, in 7 grandparents. In families of diabetic children and adolescents relatives with type 1 and type 2 diabetes were observed, with a dominance of relatives with diabetes type 2 in 2nd degree relatives.