BACKGROUND AND OBJECTIVE: To describe the microvascular features of treated, clinically regressed, or reactivated retinoblastoma lesions using an investigational portable optical coherence tomography angiography (OCTA) system. PATIENTS AND METHODS: Single-center, prospective, cross-sectional, consecutive case-series of children with previously treated retinoblastoma who underwent portable OCTA of posterior retinoblastoma lesions. RESULTS: Eight tumors from seven eyes of five children with retinoblastoma were included. Tumors with types 1 (calcified remnant, n = 3), 2 (non-calcified remnant, n = 1), and 3 (both calcified and noncalcified remnants, n = 1) regression revealed persistent intrinsic superficial vasculature on OCTA (five of five lesions; 100%). Lesions with type 4 regression (atrophic scar, n = 2) had complete vascular flow voids in the involved retina and underlying choriocapillaris. A reactivated tumor (n = 1) showed a distinct area of vascularity with prominent feeder/draining vessels. CONCLUSIONS: OCTA revealed that significant vascularity exists in inactive retinoblastoma lesions. Dilated feeder vessels may suggest continued disease activity. [Ophthalmic Surg Lasers Imaging Retina. 2020;51:43-49.].