Choroidal melanoma is a primary malignant intraocular tumor with unfavorable vital prognosis. Factors predisposing to invasion of choroidal melanoma into the optic nerve include its juxtapapillary localization, the large tumor size, its diffuse growth, the presence of necrosis in the tumor, increased intraocular pressure and the epithelioid cell type of the tumor. The authors describe the clinical case of a 31-year-old patient with a primary diagnosis of an optic nerve neoplasm. Peripapillary edema and indistinct optic disc margins were found by ophthalmoscopy. There was a slightly protruding gray-slate lesion with indistinct boundaries near the optic nerve disc. The retina was edematous with multiple merging hemorrhages. The data obtained by echography (the focus protruding both inside the eye and along the optic nerve trunk), color Doppler mapping (single own vessels in the projection of the orbital part of the mass) and computed tomography allowed for the suspicion of the primary choroidal melanoma. To clarify the nature of the process, a trans-conjunctival orbitotomy with a revision of the orbit and the optic nerve was performed. The expansion of the proximal part of the optic nerve with partial breakthrough of the optic nerve shells was revealed intraoperatively. The patient underwent enucleation with morphological and molecular genetic verification of the primary choroidal melanoma with invasion of the optic nerve. The data obtained (absence of chromosome 3 monosomy, deletion of the short arm of chromosome 1, methylation of promoter regions of the RASSF1A gene, mutations in the 4 and 5 exons of the GNAQ gene, CT genotype of the polymorphic marker C3435T of the ABCB1 gene) indicate a relatively favorable vital prognosis, despite the extrascleral growth of the tumor and its mixed cell type. The patient underwent a course of anti-relapse proton irradiation of the orbit with a total dose of 58.8 Gy at 80–90% isodose. Currently, 7 years after the treatment, the patient continues to be followed up by ophthalmologists and oncologists, without any signs of local recurrence and distant metastases. This clinical example demonstrates the possibility of extraocular extension of a small intraocular choroidal melanoma simulating an optic nerve tumor, and confirms the need for a thorough clinical and instrumental examination for a correct diagnosis and adequate management of the patient.