Forty-eight adult patients without clinical evidence of inguinal or abdominal wall hernias underwent peritoneal scintigraphy shortly after beginning continuous ambulatory peritoneal dialysis (CAPD). Scintigraphically detectable subclinical structural defects involving the inguinal canal or abdominal wall were present in 14 patients. Within 5 months, four of these defects progressed to clinically significant CAPD-related structural complications. These patients could not be distinguished by clinical or scintigraphic criteria from the 10 patients with nonprogressive structural defects. No scintigraphic structural defects were detected in 34 patients, 30 of whom remained free of CAPD-related structural complications. Five patients developed symptomatic structural complications during follow-up in areas that had been scintigraphically normal at the onset of CAPD. We conclude that some CAPD-related structural complications arise de novo, while others represent progression of subclinical pre-existent structural abnormalities that can be detected by peritoneal scintigraphy. However, most asymptomatic scintigraphic defects do not progress to a symptomatic stage, limiting the usefulness of prospective peritoneal scintigraphy as a guide to recommend prophylactic repair of all asymptomatic structural defects in patients beginning CAPD.