Objective To evaluate the clinical and histopathological features of diffuse choroidal melanoma. Methods The clinical and histopathological data of 11 patients with diffuse choroidal melanoma were reviewed retrospectively. Those patients were referred to Tianjin Eye Hospital because of visual loss or ophthalmalgia (10 cases), or Coats disease with secondary glaucoma and atrophy bulbi (1 case). The clinical disgnosis included choroidal tumor or melanoma (8 cases), absolutestage glaucoma (2 cases) and atrop hy bulbi with Coats disease (1 case). Nine patients received enucleation, and 2 patients received enucleation combined with orbital exenteration. The cellular proliferation was assessed by Ki-67staining. Results All 11 tumors had grown flatly with a wide base ranged from 12 to 20 mm, and tumor thickness ranged from 2 to 4 mm. There were 9 cases of mixed cell type, 1 case of epithelioid cell type and 1 case of necrotic cell type. The tumors invaded into the sclera in 7 cases and orbital cavity in 3 cases. Secondary glaucoma was found in 7 cases. On average, 9% (7%13%) of tumor cells were Ki67 positive and most of them located at the tumor base. There were more Ki67 positive epithelioid tumor cells than Ki67 positive spindle-shaped cells. Conclusions Diffuse choroidal melanoma had a special growth pattern and is difficult to be recognized, sometimes could be misdiagnosed as glaucoma or other choroidal tumors. With its wide base, this tumor could easily invade the orbit and metastate, and its prognosis is very poor.