Fibronectin glomerulopathy (FNG) is an inherited disease, characterized by massive fibronectin (FN) deposits in the glomeruli. We semiquantitatively analyzed glomerular lesions and their progression in 5 cases with FNG from 4 different families: a 4 year-old male, a 19 year-old female, a 27 year-old male, a 58 year-old male (the father of the former case) and a 75 year-old male. All subjects showed a 201 times higher value of mean glomerular-tuft area (GA) and a 2.0 times higher mean number of mesangial cells (No. of MC) relative to control (p < 0.001). Strong positive correlations were observed between GA and the No. of MC (r = 0.86, p < 0.001). The younger cases showed markedly higher value of GA and No. of MC than the older cases. Mean individual capillary luminal area was decreased in all but one case and the mean total capillary luminal area, which is roughly estimated as the glomerular filtration area, was less changed compared with the control. The number of capillary loops tended to increase, indicating elongation of the capillary loops. The fractional area of FN (%FN), collagen IV (%Coll. IV) and laminin (%Lam) were high in all cases except for the first Bx in the 27 year-old case. The %FN strongly correlated with %Coll. IV and %Lam (r = 0.86, r = 0.69, p < 0.001, respectively). Serial biopsy (Bx) with a 10 year-interval was examined in the 27 year-old case and his father: GA and No. of MC were increased 1.4 and 1.9 times in the son, compared with his first Bx (p < 0.001, respectively), while no change was observed in the father. The %FN, %Coll. IV and %Lam were significantly increased in their second Bx (p < 0.001). These results suggest that 1) enlargement of the glomeruli in FNG is caused by intraglomerular accumulation of FN, Coll. IV and Lam and proliferated mesangial cells, 2) there is a strong influence from the aging factor, and 3) compensatory elongation of the loops (increase in the capillary luminal area) may maintain the glomerular filtration.