A previously undescribed combination of cytogenetic abnormalities was detected in two renal cell tumors, one eosinophilic variant of the chromophilic type of renal cell carcinoma, and one oncocytoma. Both tumors shared loss of 1p material and monosomy 18. These complex changes, while being unusual, indicate that chromosome 1p rearrangements, rather than associated numerical changes, seem to play a crucial role in the development of renal tumors.