Objective To analyze the problems in the diagnosis of Coats disease and its main causes of misdiagnosis. Methods The clinical data of a group of patients with Coats diseases who had undergone indirect ophthalmoscopy, ocular fundus photography, fundus fluorescein angiography (FFA) and follow-up examination were retrospectively analyzed. The main causes of misdiagnosis were analyzed via reviewing the images of FFA and revising or confirming the initial diagnosis of Coats diseases according to the main features of abnormal dilation of retinal capillary vessels. Result In 68 patients (75 eyes), there were 45 cases whose initial diagnosis was Coats disease while the final diagnosis was not, in whom the final diagnosis was old retinal vein occlusion in 21, retinal vasculitis in 9, diabetic retinopathy in 3, old posterior uveitis in 3, congenital retinoschisis in 3, and proliferative vitreoretinopathy, familial exudative vitreoretinopathy, racemose hemangioma, old rhegmatogenous retinal detachment, macular epiretinal membrane, and idiopathic juxtafoveal telangiectasis in 1, respectively. There were 23 patients who was diagnosed as Coats disease in the final diagnosis but not the initial one. The initial diagnosis was old posterior uveitis in 6 patients, retinal vasculitis in 5, exudative age-related macular degeneration in 4, retinal main arterial tumor in 2, retinal angioma in 3, intraocular tumor in 2, and central serous chorioretinopathy in 1. Conclusions There are many problems in the clinical diagnosis of Coats disease. The main reason of misdiagnosis is that the clinicians can not comprehensively master the core of the definition of Coats disease and its clinical characters. (Chin J Ocul Fundus Dis, 2005, 21: 377-380)