['IgA nephropathy (IgAN) may progress to renal failure for some patients without any clinical risk factors and it is not unusual to find severe pathologic damage in clinically mild IgAN. We therefore investigated whether urinary kidney injury molecule-1 (KIM-1) was related to pathologic involvement in clinically mild IgAN.', 'Urinary KIM-1/creatinine of 51 IgAN patients with normotension, normal renal function and proteinuria\u2009<\u20091.0\xa0g/24\xa0h were tested. Relationships between urinary KIM-1 and pathologic features were analyzed.', 'Eighteen of the 51 patients had elevated urinary KIM-1. The tubular atrophy/interstitial fibrosis was more severe in patients with elevated urinary KIM-1 than that in patients with normal urinary KIM-1 (T0/T1/T2, 13/5/0 vs. 33/0/0, P\u2009=\u20090.004). Proportion of glomeruli containing cresecents was higher in patients with elevated urinary KIM-1 than that in patients with normal urinary KIM-1 (50% vs. 18%, P\u2009=\u20090.026). Urinary KIM-1 correlated with the proportion of total crescents (R\u2009=\u20090.303, p\u2009=\u20090.031) and fibrous crescents (R\u2009=\u20090.456, p\u2009=\u20090.001), but did not correlate with the proportion of cellular crescents or fibrocellular crescents. Although the proportion of vascular lesions was higher in patients with elevated urinary KIM-1 (44.4%) than that in patients with normal urinary KIM-1 (18.1%), the difference was not significant (p\u2009=\u20090.057). There was no difference of the response to treatment between patients with and without elevated urinary KIM-1 during a short-term follow-up.'] Is urinary kidney injury molecule-1 related to pathologic involvement in IgA nephropathy with normotension , normal renal function and mild proteinuria?