We have identified a novel gene, six transmembrane protein of prostate 2 (STAMP2), named for its high sequence similarity to the recently identified STAMP1 gene. STAMP2 displays a tissue-restricted expression with highest expression levels in placenta, lung, heart, and prostate and is predicted to code for a 459-amino acid six transmembrane protein. Using a form of STAMP2 labeled with green flourescent protein (GFP) in quantitative time-lapse and immunofluorescence confocal microscopy, we show that STAMP2 is primarily localized to the Golgi complex, trans-Golgi network, and the plasma membrane. STAMP2 also localizes to vesicular-tubular structures in the cytosol and colocalizes with the Early Endosome Antigen1 (EEA1) suggesting that it may be involved in the secretory/endocytic pathways. STAMP2 expression is exquisitely androgen regulated in the androgen-sensitive, androgen receptor-positive prostate cancer cell line LNCaP, but not in androgen receptor-negative prostate cancer cell lines PC-3 and DU145. Analysis of STAMP2 expression in matched normal and tumor samples microdissected from prostate cancer specimens indicates that STAMP2 is overexpressed in prostate cancer cells compared with normal prostate epithelial cells. Furthermore, ectopic expression of STAMP2 in prostate cancer cells significantly increases cell growth and colony formation suggesting that STAMP2 may have a role in cell proliferation. Taken together, these data suggest that STAMP2 may contribute to the normal biology of the prostate cell, as well as prostate cancer progression.