Wilms' tumor (WT), the most common kidney tumor among children, is characterized by a triphasic morphology consisting of blastemal, epithelial, and stromal components. Adult WT is a rare malignancy displaying similar histological features. We here present the first published high-resolution genomic analysis of a mixed-type adult WT. This revealed a more pronounced genetic complexity than usually observed in children with mixed-type WT. The majority of chromosomes displayed uniparental disomies, and microdeletions were present in genes with known importance for tumor formation (LRP1B, FHIT, and WWOX) or organogenesis (NEGR1 and ZFPM2), abnormalities not previously reported for pediatric WT. Our results indicate that adult WT is a biological entity distinct from the corresponding pediatric tumor type.