We describe a technique to accurately align the circumferences of the donor button and host cornea during penetrating keratoplasty. The donor cornea is trephined on a block into which four narrow, intersecting, equally spaced radial cuts are made. Suction is applied to the donor cornea through the four cuts, resulting in four radial marks in the donor corneal epithelium. Four radial marks are also made in the host cornea before trephination, using a radial keratotomy marker. When the donor button is placed within the recipient opening, the radial marks are aligned and used as guides for the cardinal sutures. This simple technique allows for matching of the donor and host circumferences, even if there is some collapse of the peripheral host cornea and sclera at surgery, and should minimize astigmatism resulting from donor/host misalignment.