B7-H4 is a recently identified B7 family member that negatively regulates T cell immunity by the inhibition of T cell proliferation, cytokine production, and cell cycle progression. In this study, we report that the genomic DNA of human B7-H4 is mapped on chromosome 1 comprised of six exons and five introns spanning 66 kb, of which exon 6 is used for alternative splicing to generate two different transcripts. Similar B7-H4 structure is also found in mouse genomic DNA in chromosome 3. A human B7-H4 pseudogene is identified in chromosome 20p11. 1 with a single exon and two stop codons in the coding region. Immunohistochemistry analysis using B7-H4-specific mAb demonstrates that B7-H4 is not expressed on the majority of normal human tissues. In contrast, up to 85%(22 of 26) of ovarian cancer and 31%(5 of 16) of lung cancer tissues constitutively express B7-H4. Our results indicate a tight regulation of B7-H4 expression in the translational level in normal peripheral tissues and a potential role of B7-H4 in the evasion of tumor immunity.