We report the detailed molecular characterization of a human parathyroid adenoma with a clonal parathyroid hormone gene rearrangement. This rearrangement is similar to one we characterized recently in an independent adenoma. In these two, plus a third partially characterized adenoma, one allele of the PTH gene, on 11p15, is rearranged with DNA from the D11S287 region on 11q13. This region contains a transcribed sequence, D11S287E, distinct from known 11q13 oncogenes, that is expressed in all parathyroid tissues examined, but is overexpressed dramatically in all three tumours with PTH gene-D11S287 rearrangements. These findings suggest that overexpression of D11S287E, perhaps driven by the misplaced PTH gene's regulatory elements, contributed to the development of these benign tumors. D11S287E is a new candidate oncogene with potential importance in parathyroid adenomas and perhaps other tumors with 11q13 abnormalities.