Coats' disease is an idiopathic disorder defined by an abnormal development of retinal vessels with a progressive deposition of intraretinal or subretinal exudates, leading to exudative retinal detachment. The most difficult task is to differentiate Coats' disease from retinoblastoma. We present a rare case of Coats' disease diagnosed in a 3-year-old girl. From the age of 6 months, the girl was followed up 2 times a year at the Department of Ophthalmology, Hospital of Lithuanian University of Health Sciences, due to congenital convergent strabismus and refractive errors. At the age of 3.6 years, a routine examination of the fundus of the right eye revealed hard exudates, telangiectasia and tortuosity, gray color lesion below the optic nerve disc, submacular exudation in the inferior nasal part of the retina, and exudative retinal detachment, which extended from the 7-o'clock position to the 4-o'clock position. Before this examination, no abnormalities were found in the fundus of her both eyes. The girl was not treated with laser photocoagulation, cryocoagulation, or intravitreal injections, as the diagnosis of retinoblastoma could not be excluded; therefore, only eye drops were prescribed. In order to exclude the diagnosis of retinoblastoma, ultrasonography, magnetic resonance imaging, and computed tomography were carried out, and an appointment to see an ophthalmic oncologist was scheduled. Due to early and appropriate treatment, the progression of Coats' disease in patients could be arrested. However, in some cases, when the diagnosis is ambiguous, it is better to follow up the patient and to treat only with eye drops.