A variety of methods for maintaining pupillary dilation for intraocular surgery have been advocated because pharmacologic agents may fail to maintain or adequately dilate the pupil. We have used a threaded needle to rapidly dilate the pupils of 19 aphakic, pseudophakic, or phakic eyes without damaging the lens or pseudophakos. This dilating suture can be constructed from available materials at low cost. We discuss the preparation of the suture and the techniques that allow rapid and reliable dilation during posterior vitrectomy or anterior segment surgery. Histologic studies were performed on rabbit eyes and demonstrated the position of the suture after performing pupillary dilation in phakic eyes. The technique has been used to dilate the pupils of phakic, aphakic, and pseudophakic patients without evidence of clinically significant complications.