The aim of the study is to evaluate the changes in kidney function after pre-emptive kidney transplantation in patients with polycystic liver and kidney disease (PLKD) and to establish whether pre-emptive kidney transplantation is warranted. Between 1998 and 2006, five patients with severe anatomical changes in both native kidneys but only mild alteration of the clearance function received combined liver and kidney transplantation. Preoperatively, Technetium-99m mercaptoacetyltriglycine (Tc99m MAG3) scintigraphy was used to evaluate separately the function of each native kidney. This examination was repeated six months after transplantation, additionally measuring the function of the transplanted kidney. Pretransplant creatinine levels were 77-115 mumol/l and Tc99m MAG3 clearance was 141-163 ml/min/1.73 sqm (74 +/- 8% of minimum-for-age values). Six months after transplant, creatinine values were not significantly different. Minimum-for-age clearance decreased by 12.5 +/- 11.5% in four patients, and increased by 26% in one patient. In four patients, the transplanted and the native kidneys assumed each about one third of total tracer clearance. In one patient, the transplanted kidney assumed 92% of the clearance function. Kidney function decreases despite pre-emptive kidney transplantation. Native kidneys are not functionally excluded and the clearance seems to be divided between native and transplanted organs. Kidney transplantation in nonuremic PLKD patients does not improve the overall kidney function and should be performed only in exceptional cases.