To determine the effect of a triamcinolone-assisted pars plana vitrectomy (PPV) on the visibility of hyaloid during surgery and the postoperative clinical outcome. Thirty-one patients with proliferative retinal disease [8 with diabetic macular edema (DME), 10 with proliferative diabetic retinopathy (PDR), 13 with proliferative vitreoretinopathy (PVR)] underwent PPV, where the vitreous body was visualized by the intravitreal injection of triamcinolone solution during the operation. The visual acuity, intraocular pressure (IOP), tamponade, corneal pathology, after-cataract, vitreous hemorrhage, and necessity of reoperation, were thereafter examined for at least 3 months after surgery. The anterior chamber laser flare cell meter was used on postoperative day 8 in DME eyes with triamcinolone-assisted PPV and with routine PPV to evaluate the breakdown of the blood-ocular barrier. The vitreous body was clearly seen by means of triamcinolone during surgery, which greatly helped us to perform a posterior hyaloid resection safely and thoroughly. Six of 8 DME eyes, 8 of 10 PDR eyes, and 5 of 13 PVR eyes showed an improvement in their vision postoperatively. No eye except one experienced IOP elevation above 21 mmHg for 7 days. Six eyes had vitreous hemorrhage. The DME eyes which received triamcinolone-assisted PPV showed significantly less breakdown of the blood-ocular barrier than those with routine PPV (Mann-Whitney U-test, P<0.01). Triamcinolone improved the visibility of the hyaloid and the safety of the surgical procedures during PPV and also inhibited the postoperative breakdown of the blood-ocular barrier. Although the long-term effects are still unknown, this method appears potentially useful as an improved treatment for proliferative retinal diseases.