In a review of 160 cases of retinopathy of prematurity (ROP), 14 patients were found to have an associated persistent hyaloid vascular system. The following four different manifestations of a persistent hyaloid system were identified: (1) hyaloid artery anastomosed to peripheral neovascularization (1 case); (2) hyaloid artery present with attached retina (3 cases); (3) fibrousappearing stalk with detached retina (3 cases); and (4) massive persistent hyaloid vascular system (7 cases). In some cases, the hyaloid artery was only an associated finding and unrelated to ROP. In other cases, the hyaloid artery appeared to be an integral component of the retrolental membrane. Recognition of a massive persistent hyaloid artery has important prognostic value because the vessels are adherent to the retina and the retrolental membrane complicating surgical repair. The role of the associated hyaloid artery in ROP is described.