A clinicopathological and morphometric analysis of glomerular hypertrophy (GH) was conducted using biopsies obtained from 52 selected pediatric patients with IgA nephropathy (IgAN). Of the 52 patients, consisting of 12 with chronic renal failure (CRF) and 40 without CRF, various clinical and morphometric parameters were compared to 10 controls with benign hematuria. The mean glomerular tuft size, mesangial area, and interstitial area all significantly increased in patients with poor prognosis when compared to the non-CRF-IgAN cases and the control cases. The glomerular capillary loop size was also significantly greater in CRF-IgAN than in non-CRF-IgAn patients (1.37 times) and the controls (1.55 times). The 10-year renal survival rates of patients with 'large' loop size (>1.55-fold) were significantly lower (p < 0.001) than those of patients with a smaller capillary loop size. The size of the capillary loops was directly related to the relative interstitial area (Aint) (r2 = 0.43, p < 0.001), to the degree of glomerulosclerosis (GS; r2 = 0.348, p < 0.001) and the mesangial area (r2 = 0.326, p < 0.001). Proteinuria tightly correlated with the capillary loop size (r2 = 0.374, p < 0.001). It was not unexpected that a strong relationship was detected between the serum creatinine level and Aint (r2 = 0.452, p < 0.001) and the percentage of GS (r2 = 0.342, p < 0.001). In IgAN the percentage of GS correlated significantly with Aint (r2 = 0.484, p < 0.001). GH, which was manifested by glomerular capillary loop dilatation, shows a close correlation with the interstitial expansion, degree of GS and mesangial enlargement. These data suggest that both extra- and intraglomerular hemodynamic changes followed by primary glomerular damage thus lead to capillary dilatation of the intact glomeruli as a morphological manifestation of GH and therefore such changes play a key role in the progression of IgAN.