Clonal chromosomal changes were detected in three of five sporadic angiomyolipomas of the kidney irrespective of a solitary or multifocal appearance of this benign tumor type. No specific chromosomal changes have been identified. Including the cytogenetic data of the four renal angiomyolipomas reported in the literature, trisomy 7 as the single clonal chromosomal abnormality was detected in two angiomyolipomas. Because trisomy 7 has been reported in both neoplastic and nonneoplastic kidney cells, it may be assumed that trisomy 7 is already physiologically resident in renal cells but undergoes positive selection in this tumor type.