Acquired renal cystic disease develops in the native kidneys of patients with renal allografts with long-standing poor function. However, there has been no long-term prospective study of the regression or development of cysts in native kidneys of renal allograft recipients with good long-term function (serum creatinine: 114 +/- 24 mumol/l). We followed 61 renal allograft recipients for 63.5 +/- 29.0 months (mean +/- SD) using computed tomography (CT scan) every 1 or 2 years after transplantation. The cyst grade at pretransplantation was significantly reduced at the first study after transplantation (0.98 +/- 1.39 vs. 0.57 +/- 0.96; p less than 0.01). Baseline study after transplantation revealed that the incidence of cysts in native kidneys was 22/61 (36.1%) and 26/61 (42.6%) in the follow-up study. In 32 patients (52.5%), there were no visible cysts in the native kidneys. In 9 patients (14.8%), there was no change in the number of cysts during follow-up, while in another 9 patients the number of cysts decreased. On the other hand, the number of cysts increased in 11 patients (18.0%) during follow-up. The mean follow-up duration was longer in the group with an increased number of cysts than in the groups with no visible cysts or a decrease in number. Biochemical analysis of cyst fluid from newly developed cysts in 2 patients showed differences from the pattern in acquired renal cystic disease of hemodialysis patients. These results indicate that after regression of acquired cysts in most allograft recipients, no or only a few cysts persist in patients with good graft function. The remaining cysts continue to regress further in some patients.(ABSTRACT TRUNCATED AT 250 WORDS)