Beckwith–Wiedemann syndrome (BWS) and isolated hemihyperplasia (IHH) are two well known overgrowth conditions that are associated with cancer predisposition. Multiple surveillance protocols have been proposed to detect the most commonly reported tumor types Wilms tumor and hepatoblastoma. We reviewed the history of our patients who were part of this monitoring protocol. Information from 63 cases was collected retrospectively while another 63 control samples for AFP measurement were obtained prospectively. Twenty-five (40%) patients had an ultrasound abnormality, the most frequent being nephromegaly/size discrepancy. Two patients had well documented cases of tumors/tumor precursor (2/63:3.2%) detected by ultrasound images. Three hundred thirty-six separate AFP values were available with values above 50,000 ng/ml seen in three patients older than 2 months, one with hepatoblastoma and two other with hemangiomas/hemangioendotheliomas. There was no clear difference in the range of AFP values between previously reported controls, our own normal population and affected patients. In conclusion, ultrasound surveillance detected renal and liver pathology including benign and malignant lesions. The known variability of AFP in normal neonates and patients with BWS makes interpretation difficult in early infancy. Very high AFP values did seem to be correlated with risk for identifiable liver lesions. Determination of the natural changes in AFP levels over time will allow more appropriate comparison. © 2009 Wiley-Liss, Inc.