Objective To analyze the clinical risk factors and prognosis of elderly peritoneal dialysis patients with peritonitis. Methods A retrospective analysis was conducted on the data of patients who underwent peritoneal dialysis and developed peritonitis at this peritoneal dialysis center between January 2020 and November 2022. Patients were divided into 2 groups according to their age at peritonitis onset: an elderly peritonitis group (age≥65) and a non-elderly peritonitis group (age<65). General information and peritonitis-related data were collected, and the clinical risk factors and prognosis of peritonitis between the 2 groups were compared. Results A total of 62 patients with peritonitis were enrolled, including 26 in the elderly peritonitis group, where the median age was 71 (range 65-88), 12 patients were male (46.2%), and 5 patients had diabetic nephropathy complicated by diabetes mellitus (19.2%); 36 in the non-elderly peritonitis group, where the median age was 48 (range 26-63), 23 patients were male (63.9%), and 5 patients had diabetic nephropathy complicated by diabetes mellitus (13.9%). The elderly peritonitis group exhibited a worse prognosis than the non-elderly peritonitis group (mortality 30.8% vs. 2.8%; technique failure rates 23.1% vs. 16.7%, P=0.004). The elderly peritonitis group had a higher proportion of patients with education level of middle school or below (72.2% vs. 53.8%, P=0.038), a higher proportion requiring caregivers (100% vs. 83.3%, P=0.035), a higher frequency of operator changes (38.5% vs. 11.1%, P=0.011), longer initial training time (4 d vs. 3 d, P<0.01), and longer dialysis duration (70.5 months vs 29.5 months, P=0.002). The non-elderly peritonitis patients had better nutritional status: both normalized protein catabolic rate (nPCR) (0.90 vs. 0.79, P=0.007) and plasma albumin (34.78 g/L vs. 30.77 g/L, P<0.01) were higher. The elderly peritonitis group had lower levels of blood creatinine (872.42 μmol/L vs. 1053.69μmol/L, P<0.01), blood uric acid (345.0 μmol/L vs. 372.0 μmol/L, P=0.023), blood potassium (3.65 mmol/L vs. 3.95 mmol/L, P=0.012), blood phosphorus (1.54 mmol/L vs. 1.80 mmol/L, P=0.022), intact parathyroid hormone (iPTH) (227.2 pg/mL vs. 414.0 pg/mL, P=0.037), and 25-hydroxyvitamin D₃ (17.95 nmol/L vs. 22.57 nmol/L, P=0.007). Conclusions Elderly patients with peritonitis had a poorer prognosis. Compared with younger patients with peritonitis, elderly patients had lower education levels, longer dialysis duration, worse nutritional status, poorer operational ability, and a greater need for caregivers.