PRAD1 (cyclin D1) is a recently identified member of the family of cyclin genes, believed to play roles in regulating transitions through the cell cycle. The PRAD1 gene, located at 11q13, has been implicated in the pathogenesis of a variety of tumors, including parathyroid adenomas, t(11;14) bearing B-lymphoid tumors (particularly centrocytic lymphomas) where it is highly likely to be the BCL1 oncogene, and possibly in breast carcinomas and squamous cell cancers of the head and neck as well. PRAD1's tumorigenic influence appears to be effected through overexpression of its normal-sized transcript, but it has not been established whether the transcript's coding sequence is normal or contains oncogenic mutations. We have sequenced the coding region of the overexpressed PRAD1 transcript from two primary tumors with clonal PRAD1 region rearrangements: a benign parathyroid adenoma and a malignant centrocytic lymphoma. Each sequence is identical to the normal PRAD1 cDNA sequence, and presumably encodes normal PRAD1 protein. Thus, PRAD1 likely functions as a direct-acting oncogene whose rearrangement in tumors leads to overexpression or deregulated expression of its normal protein product.