Abstract: An implantable prosthesis for repairing a tissue or muscle wall defect. The prosthesis includes a perforated sheet of a biologically compatible material to cover the tissue or muscle wall defect. The perforated sheet has a plurality of perforations extending through the sheet. The perforations may be distributed across the perforated sheet in a non-grid arrangement. The perforations may be non-uniformly distributed across the perforated sheet in groups of perforations arranged in a plurality of concentric circular patterns. Each perforation may be separated from an adjacent perforation by a web of material having a length between adjacent perforations that is a predetermined multiple of the diameter of the perforations.