Microvascular flow imaging (MFI) is a recently developed ultrasound technique that aims to show small vessels and slow blood flow without using contrast agents. In MFI, a novel clutter suppression algorithm is applied to separate slow flow signals from tissue motion artifacts. MFI can image vessels as small in diameter as 0.1 mm and flow velocities as slow as 1 cm/s. In this preliminary study, MFI was used to image 20 eyes referred for possible retinoblastoma: 13 eyes were diagnosed with retinoblastoma, six eyes with persistent fetal vasculature (PFV), and one eye with medulloepithelioma. MFI reliably showed fibrovascular distribution in PFV and modified the classification of PFV. In retinoblastoma eyes, MFI reliably showed the intrinsic vascular pattern, which cannot be imaged by fluorescein angiography. We recommend that ophthalmologists use MFI as an adjunctive imaging modality to traditional color Doppler imaging.