Little data are available about risk factors for peritoneal catheter subcutaneous tunnel infection. Therefore, we analyzed tunnel infections occurring in our program over a 10.5-year period. One hundred twenty-nine tunnel infections occurred in 92 of 411 patients (22%) on peritoneal dialysis for a mean of 19 ± 19 months. Tunnel infection rate was 0.19 per year. By 1 year, 15% of patients had a tunnel infection, and by 2 years, 23%. Tunnel infection rates decreased with increasing time on peritoneal dialysis: 2.4 per year for patients on peritoneal dialysis less than 1 year, 0.8 per year for patients on dialysis 1 to 2 years, and 0.4 per year for patients on dialysis greater than 2 years (all different at P < 0.01). Organisms were cultured in 109 tunnel infections: gram-positive cocci in 77 episodes (71 %) [Staphylococcus aureus 57, 52%], and gram-negative bacilli in 24 episodes (22%). Tunnel infection rates were higher in diabetics than in nondiabetics (0.27 per year v 0.16 per year, respectively; P < 0.001 by life-table analysis of time to first infection) and also higher in women than in men (0.23 per year v 0.17 per year, P < 0.001). Tunnel infection rates were 0.35 per year for diabetic women, 0.20 per year for diabetic men, 0.18 per year for nondiabetic women, and 0.15 per year for nondiabetic men (groups different, P < 0.001). Race and age were similar in patients with and without tunnel infections. Catheter loss was 80% when tunnel infection was associated with peritonitis and 40% when tunnel infection alone was present (P < 0.001). We conclude that the risk of tunnel infection is highest early in the course of peritoneal dialysis and that diabetic women, for unclear reasons, are at the highest risk.