Primary peritonitis is a well-described infectious complication of nephrotic syndrome. Current data on the true incidence of peritonitis and efficacy of preventive pneumococcal vaccination are not clear in this group of children. In this nationwide study, among a total of 268 patients with an initial diagnosis of steroid sensitive nephrotic syndrome, eight episodes of primary peritonitis were detected in seven patients during 5 years. All eight attacks of peritonitis occurred in the relapse period. Seven of these peritonitis episodes occurred in the first 2 years of nephrotic syndrome, three of them during the first attack. One patient had two attacks with a 6-month interval. Only two of the patients were steroid sensitive, while four of them were steroid dependent, and one was steroid resistant at the diagnosis of peritonitis. The causing microorganism was identified in three patients (Streptococcus hemolyticus, Streptococcus pneumoniae, and alpha-hemolytic Streptococcus). Incidence of peritonitis (2.6%) in our series was not high when compared with previous reports. None of the patients had been immunized against pneumococcus before or after the peritonitis attack. It raises the question if the vaccine is necessary for every child with steroid sensitive nephrotic syndrome. However, we suggest that immunization against pneumococcus is not indicated in children with steroid-responsive nephrotic syndrome (NS) and should be reserved for the small number of children who have steroid-dependent or steroid-resistant NS.