Prostate cancer (PC) commonly metastasizes to the bone, resulting in pathologic fractures and poor prognosis. CCN3/nephroblastoma overexpressed is a secreted protein with a known role in promoting breast cancer metastasis to bone. However, in PC, CCN3 has been ascribed conflicting roles; some studies suggest that CCN3 promotes PC metastasis, whereas others argue a tumor suppressor role for CCN3 in this disease. Indeed, in the latter context, CCN3 has been shown to sequester the androgen receptor (AR) and suppress AR signaling. In the present study, we demonstrate that CCN3 functions as a bone-metastatic mediator, which is dependent on its C-terminal domain for this function. Analysis of tissue microarrays comprising >1500 primary PC patient radical prostatectomy specimens reveals that CCN3 expression correlates with aggressive disease and is negatively correlated with the expression of prostate-specific antigen, a marker of AR signaling. Together, these findings point to CCN3 as a biomarker to predict PC aggressiveness while providing clarity on its role as a functional mediator of PC bone metastasis.