PURPOSE:To report a case of unilateral endogenous Streptococcus anginosus endophthalmitis in order to improve timely recognition and treatment strategies for similar presentations. METHODS:A retrospective review of the electronic medical record of one patient was performed from September 2024 through December 2024. RESULTS:A 50-year-old healthy male presented with a unilateral hypopyon and dense vitreous opacities. The patient was found to have evidence of systemic infection and endophthalmitis secondary to S. anginosus; specifically, the patient was found to have a large subcarinal mass as well as abscesses in the left cerebrum, both of which were positive for S. anginosus. The patient underwent treatment with intravitreal and systemic antibiotics as well as pars plana vitrectomy. CONCLUSION:S. anginosus endophthalmitis in the setting of a confirmed primary mediastinal infection has not previously been reported. Our patient had a particularly virulent presentation of S. anginosus endophthalmitis, and the ophthalmic findings led to the diagnosis of a systemic infection. A thorough systemic evaluation of patients with suspected endogenous endophthalmitis should be pursued, and a seemingly noncontributory medical history can prove to be significant.