Hematuria is the usual urinary finding in patients with diabetic nephropathy. In this study, prevalence and significance of microhematuria in patients with diabetes mellitus were investigated.Five hundred and forty-two samples from outpatients, who consulted the Department of Diabetes and Metabolism, were categorized into 4 groups according to the results of the urine dipstick test. Group I :258 samples, urinary protein(u-P) 1+ and occult blood (OB) negative, group II: 95 samples: u-P 1+, OB 1+ approximately 3+, group III: 89 samples: u-P 2+ approximately 3+, OB negative, group IV 100 samples u-P 2+ approximately 3+, OB 1+ approximately 3+.Serum concentrations of creatinine and highly sensitive CRP were both significantly higher in group II than in group I . Those parameters were also significantly higher in group IV than in group III.These results indicate that a positive dipstick test for OB may occur in many patients with diabetes mellitus and suggest the progress of renal damage.