In recent adult literature, there have been reports of an increasing incidence of focal segmental glomerulosclerosis (FSGS) among patients with nephrotic syndrome. To examine whether this observation is also relevant to the pediatric population we utilized our hospital computerized database to analyze the data on children with primary nephrotic syndrome seen first between the years 1984 and 1995. A questionnaire was also sent to all metropolitan Kansas City pediatricians to identify possible patients outside the database. The inclusion criteria were clinical nephrotic syndrome or proteinuria with a kidney biopsy. A total of 148 patients (group A) were identified; 86 of them from metropolitan Kansas City (group B). In group A the incidence of minimal change disease (MCD) and FSGS was 52.7% [95% confidence interval (CI) 44%-60%] and 23.0% (95% CI 16-29%), respectively and in group B 54.7% (95% CI 44%-65%) and 24.5% (95% CI 15%-33%), respectively. Those numbers were significantly different from the International Study of Kidney Disease in Children (IS-KDC) reported incidence of 76.4% for MCD and 6.9% for FSGS. Similar to the ISKDC, in our population children over 6 years had a higher incidence of FSGS than younger children (32.8% vs. 16.7%, P = 0.028). The annual incidence rate for nephrotic syndrome in group B was 2.2 cases/10(5) children per year, of which MCD comprised 1.22 cases/10(5) children per year and FSGS 0.5 cases/10(5) children per year. The annual incidence rates of both primary nephrotic syndrome (3.6) and FSGS (1.6) were significantly higher in African-Americans, than Caucasians (1.8 and 0.3 cases/10(5) children per year, respectively). Our study indicates nearly no change in the annual incidence of pediatric primary nephrotic syndrome, but a higher incidence of FSGS with reciprocal decline in the incidence of MCD. The possibility of primary nephrotic syndrome being caused by a non-MCD entity is further raised among African-American and in children over 6 years. We conclude that our perception of primary nephrotic syndrome of childhood as a benign condition has to be carefully reexamined and a more-guarded prognostic approach adopted in our geographic area.