A 50-year-old man presented with visual disturbance at a local ophthalmology clinic. He was given a diagnosis of uveitis and treated with oral corticosteroids; however, his visual disturbance did not improve and he was admitted to our hospital. A chest CT scan showed a pulmonary nodule in the upper lobe of the right lung, and right hilar and mediastinal lymphadenopathy. Transbronchial biopsy yielded a diagnosis of squamous cell carcinoma, and an ophthalmologic examination revealed bilateral diffuse uveal melanocytic proliferation (BDUMP). BDUMP is a rare manifestation of paraneoplastic syndrome, and the characteristics of the condition have not yet been clarified in detail. BDUMP carries a very poor visual prognosis, and in the present case, the patient's visual disturbance progressed rapidly despite systemic chemotherapy and corticosteroid therapy.