In Caucasian patients with insulin-dependent diabetes mellitus (IDDM) proliferative diabetic retinopathy (PDR) and persistent proteinuria (PP) are associated, and major risk factors for development of microangiopathy have been identified. The aim of the present study was to evaluate whether these risk factors are also relevant and whether an association exists between the microangiopathic complications in Japanese IDDM-patients. A clinic-based cohort of 324 Japanese IDDM-patients was followed (a mean follow-up of 7 years). Annual examination for development of PDR and PP was performed. Fifty-eight patients developed PDR and 24 developed PP. Development of PDR was associated to high HbA1c-levels, i.e., the 4th quartile (RR 7.9, P < 0.0001), background retinopathy at admission (RR 9.9, P < 0.0001), high age at diabetes onset (RR 2.9, P < 0.0001) and female gender (RR 1.7, P < 0.05). Development of PP was associated to high HbA1c-levels (RR 2.8, P < 0.001) and background retinopathy at admission (RR 7.9, P < 0.0001). The risk of developing PP was 9 times higher in patients developing PDR than in patients not developing PDR (P < 0.0001). The effect of metabolic control in our cohort was similar to that found in the DCCT and SDIS studies. In conclusion, development of PP is closely associated with PDR, also in Japanese IDDM-patients. The effect of metabolic control is the same as in Caucasian patients. Development of malignant angiopathy in IDDM-patients is not confined to Caucasian IDDM-patients, and the incidence rates are comparable to those found in Caucasian IDDM.