The aim of this study was to evaluate the role of HLA (human leucocyte antigen) class I (A, B, C) and class II (DR) alleles and familial insulin-dependent diabetes mellitus as possible risk markers for early retinopathy in a population of 103 Finnish adolescents with type I diabetes mellitus for 3.6-16.2 years. Fifty-one of the patients (49.5%) had signs of retinopathy in fundus photographs. HLA DR1 was found in 31% of the subjects with retinopathy, but in only 5% of those without retinopathy (p = 0.02). The corresponding figures for HLA DR1/4 were 17% and 2.6%, respectively (p = 0.22). The frequency of HLA DR3, DR4, or DR3/4 heterozygosity did not differ between the two groups of patients. Signs of early retinopathy showed thus an association with the presence of the HLA DR1 allele, and a mild protective effect of the HLA A9 and B40 alleles was indicated. Other HLA A, B, C, or DR alleles did not have any effect on the risk for early development of retinopathy, neither had a positive family history of type I diabetes.