Background/Aim: Focal segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome. Although the pathogenesis is not known, recent studies suggest that FSGS may be a podocyte disease. The aim of this study was to look for podocyte injury in this disease, using measurements of urinary podocytes. Methods: We examined the first morning urine of the day collected from 71 patients (45 men and 26 women, median age and range 11.2 and 3–29 years) diagnosed as having nephrotic syndrome. Freshly voided urine samples were examined by immunofluorescence labeling using monoclonal antibodies against human podocalyxin. Renal histological examinations were performed in 58 of the 71 patients: 28 had minimal-change disease, 20 had FSGS, and 10 had membranous nephropathy. Results: Median and range of urinary podocytes measured were 0.2 and 0–40.8 cells/ml for 71 patients with nephrotic syndrome and 0 and 0–0.8 cells/ml for normal healthy control subjects (n = 200). Patients with FSGS had significantly higher levels of urinary podocytes (median and range 1.3 and 0–40.8 cells/ml) than those with minimal-change disease (median and range 0 and 0–6.9 cells/m; p = 0.003) or membranous nephropathy (median and range 0 and 0–1.4 cells/ml; p = 0.02). Conclusions: The urinary excretion of podocytes is significantly higher in patients with FSGS as compared with those having membranous nephropathy or minimal-change disease. These findings suggest that podocyte injury and loss in the urine may have an important role in the pathogenesis of FSGS.