OBJECTIVE To observe the expression of thrombospondin-1 (TSP-1) in prostate cancer, and examine its expression in relation to angiogenesis.METHODS The expression of TSP-1 and microvessel density (MVD) were studied in 22 prostate cancer patients by using immunohistochemistry.RESULTS Positive expression of the TSP-1 protein was detected in 16(72.7%)of the 22 cases. Most of the positive staining for TSP-1 was seen in the cytoplasm of the cancer cells, but some was in the extracellular matrix. The mean MVD in the 22 prostate cancer cases was 71.21±31.14vessels per 100 high field of vision. Tumors with an elevated expression of TSP-1 showed a high MVD resulting in a correlation between TSP-1immunopositivity and microvessel density that was highly significant (r=0.54, P=0.009).CONCLUSION TSP-1 is strongly expressed in most prostate cancers and is associated with neovascularization. Therefore TSP-1 is a likely contributor to the extensive neovascularization in prostate cancer and increased TSP-1 expression might participate in an angiogenic phenotype.