In a review of the autopsies and medical records of 22 obese patients, focal segmental glomerulosclerosis (FSGS) was present in seven. The FSGS was mild in all but one patient. The FSGS of obese patients has similar features to idiopathic FSGS; however, our findings suggest that it lacks the hyperplasia of glomerular epithelial cells, shows no predilection for the corticomedullary junction, and is probably more often seen in the hilar region of the glomeruli. FSGS or glomerulomegaly was not associated with the degree of obesity. We demonstrated lipid deposition in the kidney of obese patients. Obese patients with FSGS, compared to those without FSGS, had higher blood cholesterol (P < 0.10) and higher triglyceride levels (P < 0.01). The mean heart weight of obese patients with FSGS was greater than that of patients without FSGS (P < 0.01). Also, obese patients with FSGS had larger glomeruli (246 +/- 33 microns) than obese patients without FSGS (218 +/- 16 microns) (P < 0.05). These findings suggest that cardiomegaly with hemodynamic changes and glomerular hyperfiltration may play a significant role in the glomerulomegaly and FSGS of obese patients. The secondary or contributory role of lipids in the development of the FSGS of obese patients remains to be determined.