The value of the use of biomaterials for the repair of abdominal wall hernias is gaining increasing recognition. The use of synthetic mesh to achieve a tension-free repair has resulted in a significant reduction in postoperative pain, in length of the recovery period, and in the number of recurrences. However, certain physical properties of biomaterials can lead to undesirable consequences. These include increased risk of infection, seroma formation, biomaterial-related intestinal obstruction, and fistula formation and failure of repair due to shrinkage of the mesh. The purpose of this paper is to discuss the mechanism of these problems with special emphasis on pore size, molecular permeation and shrinkage of biomaterials and their effects on infection, seroma formation, and recurrence of mesh repair of abdominal wall hernias.