Background: To describe the relationship between proteinuria, hematuria, and renal insufficiency, on one hand, and glomerular pathology, on the other hand, in a consecutive biopsy series of diabetic patients. Subjects and Methods: All diabetic subjects (n = 200) biopsied from 1979 to 1995 at Tampere University Hospital were identified in retrospect. The clinician-based indication (any unexplained renal finding) for renal biopsy was consistent during the years and was: proteinuria alone in 68%; combined with hematuria in 10%; with renal insufficiency in 10%; with both in 9%, and with isolated hematuria or renal failure in 3%. One third of the subjects had proteinuria of ≧3 g/24 h and 16% a serum creatinine level of ≧200 µ M. Glomerulopathy was found in 171 specimens and defined as nodular diabetic (group A), diffuse diabetic (group B) and primary (group C). The 24-hour urinary protein excretion rate [mean (range)] was 3.5 (1.6–6.9), 1.0 (0.5–3.5), and 3.6 (1.1–6.6) g in groups A, B and C, respectively (ANOVA p = 0.001). The corresponding serum creatinine values [mean (SD)] were 175 (115), 105 (142) and 169 (138) µ M (p = 0.001). Results: Nodular diabetic glomerulopathy was found in 40%, diffuse diabetic glomerulopathy in 42% and primary glomerulopathy in 18%. A primary glomerulopathy was found in any indication and in both types of diabetes (prevalence range 14–26%). The best multivariate logistic regression model obtained (χ<sup>2</sup> = 13.5, p = 0.008) in predicting the presence of diabetic glomerulosclerosis (group A + B) in contrast to a primary glomerulopathy (group C) included retinopathy (p = 0.04), renal insufficiency (p = 0.03), hematuria (p = 0.12) and type of diabetes (p = 0.10). Conclusion: In this series of diabetic subjects, biopsied due to proteinuria, hematuria and not severe renal insufficiency, 18% had evidence of a primary glomerulopathy.