To evaluate choroidal osteoma for tumor growth, tumor decalcification, related choroidal neovascularization, visual acuity loss, and poor visual acuity. Retrospective nonrandomized single-center case series. Ocular Oncology Service at Wills Eye Hospital, Thomas Jefferson University, Philadelphia, Pa. There were 74 eyes of 61 patients with choroidal osteoma evaluated between January 1, 1977, and January 1, 2003. The 5 outcome measures included tumor growth, tumor decalcification, related choroidal neovascularization, visual acuity loss of 3 or more Snellen lines, and poor visual acuity of 20/200 or worse. At 5 and 10 years, Kaplan-Meier analysis revealed tumor growth in 22% and 51% of eyes, tumor decalcification in 28% and 46% of eyes, choroidal neovascularization in 31% and 31% of eyes, visual acuity loss in 26% and 45% of eyes, and poor visual acuity in 45% and 56% of eyes, respectively. The clinical factor predictive of tumor growth was absent overlying retinal pigment epithelial alterations. The factor predictive of decalcification was irregular tumor surface. Of the 15 tumors that showed partial decalcification at the first visit, there was no further tumor growth in any case. Of the remaining 12 tumors that later developed decalcification, tumor growth, if it occurred, was along the margin opposite the decalcification. No tumor showed growth in the region of decalcification. Factors predictive of choroidal neovascularization included irregular tumor surface and subretinal hemorrhage. In 6 eyes that had both choroidal neovascularization and tumor decalcification, the neovascularization was detected prior to or at the same time as the decalcification. The factor predictive of visual acuity loss was presence of subretinal fluid whereas the factors predictive of poor visual acuity included symptoms and tumor decalcification. A comparison of eyes with subfoveal vs extrafoveal choroidal osteoma showed poor visual acuity in 15 (34%) of 44 eyes and 3 (10%) of 30 eyes, respectively. Eyes with decalcified choroidal osteomas manifested poor visual acuity in 13 (48%) of 27 eyes whereas those with nondecalcified tumors showed poor visual acuity in 5 (11%) of 47 eyes. Choroidal osteoma showed evidence of growth in 51% of eyes and decalcification in nearly 50% of eyes by 10 years. Tumors with any degree of decalcification at the initial visit showed no further growth. Overall, poor visual acuity of 20/200 or worse was found in 56% of eyes by 10 years, and decalcified subfoveal choroidal osteomas displayed a particularly poor visual prognosis.