To determine the prevalence of acquired cystic kidney disease (ACKD), as reported in adults receiving long-term hemodialysis treatment, we studied 48 pediatric patients (aged 17 +/- 5.1 years) with end-stage renal disease by high-resolution ultrasonography or magnetic resonance imaging or both. Forty patients (83%) had a functioning renal transplant, with a mean transplant survival time of 3.4 years (range, 0.3 to 14.8 years); four patients were treated by hemodialysis and four by peritoneal dialysis. The mean duration of end-stage renal disease was 5.7 +/- 3.8 years. Ultrasonography detected ACKD in 12 (29%) of 42 patients, solitary cysts in 14 patients (33%), and no cysts in 16 patients (38%). In contrast, ACKD was diagnosed in only 3 of 37 patients studied by magnetic resonance imaging. In 31 patients studied by both imaging techniques. ACKD was diagnosed in three patients by magnetic resonance imaging but in 11 by ultrasonography. In patients with ACKD, the duration of end-stage renal disease was significantly longer, but renal (transplant) function was not different from that in patients with solitary cysts or no cysts. One patient with a history of 12 1/2 years of hemodialysis had multiple renal tumors that were diagnosed as renal cell carcinomas after bilateral nephrectomy. These results indicate that young patients with end-stage renal disease should be monitored regularly for the presence of ACKD, preferably by ultrasonography, even after successful renal transplantation.