Catheter-related infection is one of the most important causes of technical dropout in peritoneal dialysis patients. Both the type of cultured organism and the extent of inflammation are well known prognostic factors for the outcome of these infections. From December 1994 to November 1996, 96 catheter-related infections without simultaneous peritonitis occurred in 49 of 86 peritoneal dialysis patients treated in this study. During the observation period, only single-cuff catheters were used. Staphylococcus aureus was the most common organism cultured (51%). Involvement of the tunnel was diagnosed by sonography in 57.1% of all Staphylococcus aureus cases, but only in 26.1% of Staphylococcus epidermidis-related exit-site infections. Ten of the 96 catheter-related infections (10.4%) resulted in catheter loss. Catheter removal was necessary only in cases of deep tunnel infection caused by Staphylococcus aureus. The number of gram-negative catheter infections was too small to allow conclusive analysis. Although sonography of the catheter tunnel is now well established in the early diagnosis of tunnel infections, no clear guidelines exist for management of these infections. In this study, patients with deep tunnel infection who did not require catheter removal showed a significant decline of the hypoechogenic area around the cuff (from 7.02 +/- 0.70 to 3.75 +/- 1.04 mm, P < 0.002) 2 wk after initiation of therapy. No significant decline was observed in patients who later lost their catheters. On the basis of these data, it is concluded that in cases of exit-site and superficial tunnel infection, conservative treatment should be performed. In cases of deep tunnel infection without peritonitis caused by Staphylococcus aureus, antibiotic treatment should be started and sonographic examination should be performed every second week. If the hypoechogenic area around the cuff decreases (> 30%), conservative treatment should be prolonged. In cases without sonographic improvement (< 30%) 2 wk after therapy, catheter removal is recommended.