Aim: Peritonitis is the most common complication of peritoneal dialysis (PD). This study aimed to investigate changes in the incidence, risk factors, microbiology, and clinical outcomes of PD-associated peritonitis in the past decades. Methods: This was a retrospective study that included children who initiated chronic PD at our institution between 2000 and 2017. The patients were divided into two groups according to the year of initiation: those who initiated PD between 2000 and 2008 and those who initiated PD between 2009 and 2017. The incidence and characteristics of peritonitis were compared between the groups. Results: A total of 184 patients with a median age of 10.2 years were included in this study. Of the patients, 92 experienced 210 episodes of peritonitis. The incidence rate of peritonitis decreased from 0.35 to 0.21 episodes/patient year during the study period (P = 0.001). During the 2000–2008 period, the 2-year peritonitis-free survival rate was significantly lower for patients under 2 years of age than for the other age groups (P = 0.004), whereas this was not observed during the 2009–2017 period. The multivariable Cox proportional hazard model showed that the <2 years age group had a significantly higher risk of developing peritonitis in the 2000–2008 period. However, this was not evident in the 2009–2017 period. Conclusions: The incidence of PD-associated peritonitis decreased, particularly in children under 2 years of age. Thus, younger age may not be a risk factor for PD-associated peritonitis.