Purpose: To investigate the expression of thrombospondin 1 (TSP-1) in retinal pigment epithelium (RPE) and choroidal neovascular membranes (CNVMs) from patients with age-related macular degeneration (AMD).Methods: Tissue sections from normal human fetal and adult eyes and surgically removed CNVMs were immunostained for TSP-1 localization. Polymerase chain reaction and Western blotting were used to analyze TSP-1 mRNA and protein from human RPE cells, respectively. TSP-1 in the supernatant of cultured RPE cells and eye explants were measured using enzyme-linked immunosorbent assay. MTT assay was used to evaluate the RPE survival after TSP-1 treatment.Results: The strongest immunostaining for TSP-1 was observed in the RPE monolayer around drusen in early AMD. The intensity of TSP-1 staining in normal eye sections was much weaker than that of early AMD and CNVM. TSP-1 mRNA was positive in cultured fetal and adult RPE cells. There was increasing secretion of TSP-1 into the supernatant of cultured RPE and eye explants. The specific band of TSP-1 was identified by Western blot. No significant inhibition of RPE survival was found with the exposure to TSP-1.Conclusions: TSP-1 expression in drusen and CNVM was upregulated and associated with RPE monolayer. TSP-1 may be a natural negative regulator for choroidal neovascularization.