OBJECTIVE To report a rare case of a unilateral choroidal mast cell infiltration in a patient with aggressive systemic mastocytosis (ASM). METHODS The patient is a man in his fifties with a diagnosis of ASM. He developed visual complaints in the right eye associated with an area of subretinal fluid on fundus examination. Visual acuity at presentation was 20/150 in the right eye and 20/25 in the left eye. After ophthalmic and radiologic imaging workup, the patient was diagnosed with presumed choroidal mast cell infiltrate. The index of suspicion was high due to the prior ASM diagnosis. External beam radiation and intravitreal injection treatments were offered but the patient declined. The patient was switched from interferon to a new targeted systemic therapy for ASM, midostaurin. Despite some mixed, temporary response in systemic symptoms/signs of ASM at four months, the choroidal lesion and subretinal fluid were stable with visual acuity at 20/125. CONCLUSIONS Mast cell choroidal infiltration in ASM should be considered as part of the differential with acute/subacute vision changes. Diagnosis requires exclusion of other possibilities with ocular imaging and in this case, monitoring for development of other malignancies in which there were none. Midostaurin's ocular response was not on par with systemic response. Additional localized ocular therapies may be required.