A 2‐year‐old Basset hound with unilateral persistent hyperplastic tunica vasculosa lentis and primary vitreous is described. There was leukokoria in the left eye, caused by bluish‐white polar densities and haemorrhagic discoloration in the nucleus of the lens. Ultrasonographic examination of the eye revealed a small hyperechoic lens and a hyperechoic linear soft‐tissue strand extending from the posterior pole of the lens through the optic disc. Power Doppler imaging revealed blood flow in this persistent hyaloid artery, but 5 months later, immediately prior to surgery, there was no flow in this artery. Ultrasonography, including Power Doppler imaging, was useful to confirm the diagnosis and to estimate the complications of surgery, especially the risk of vitreal haemorrhage after cutting of the persistent hyaloid artery. Comparison of the ultrasonographic images with those obtained by computed tomography suggested that the resolution of computed tomography is inadequate for identifying structures as fine as a persistent hyaloid artery.