Clinical, biochemical, and sonographic evaluation of the remaining kidney function and size was performed in 34 patients, 12 males and 22 females, ages 2.1–19.6 years, nephrectomized for Wilms' tumor at least 2 years before (mean 8.6). All patients had normal blood pressure and serum bicarbonates. Two of them had microhematuria, four proteinuria 4 mg/m2/hr, and 11 microalbuminuria (MA) >20 mg/24 hr. Only one patient had reduced creatinine clearance and maximum bipolar length (MBL) as well as kidney volume (KV) <100% of expected. In the other patients, average MBL was 128 ± 14% and KV was 213 ± 11% (P = 0.0001). MBL, but not KV, was inversely correlated (P = 0.04) to age at NP. KV, but not MBL, was directly correlated (P = 0.009) to MA. Average MA was 48 ± 94 mg/24 hr and was correlated to the time from NP (P = 0.026). The remaining kidney increases in volume much more than in length. The increase in KV is related to the degree of MA, whereas the increase in MBL is higher in subjects younger at NP. The high prevalence of significant MA, which is in turn related to the time from NP and to the KV, raises some concerns about the long‐term renal prognosis of children NPWT. © 1996 Wiley‐Liss, Inc.