The late appearance ofincisional hernias several years after laparotomy and the high recurrence rates after operation strongly imply the presence of a disorder of the connective tissue, although a specific defect in patients with incisional hernias has not yet been identified. In the present study we used both immunohistochemistry and Western blot analysis to evaluate the ratio of collagen I and III and the expression of the metalloproteinases (MMP) 1 and 13 in the fascia of patients with incisional or recurrent incisional hernias. Samples of healthy skin or stable skin scar in patients without hernias served as controls. Altogether, our data indicated a significantly decreased ratio of collagen I/III in the fascia of patients with incisional hernias and recurrent incisional hernias. Furthermore, in these patients the expression of MMP-1 was decreased compared to the controls, whereas MMP-13 could not be detected in any fascia sample, with or without hernias present. For the first time, our results give evidence of the existence of a possible collagen disorder in these patients. The decreased ratio ofcollagen I/III is explainable due to a relative increase of collagen type III, which is known to be characterized by thin fibril diameters and lowered mechanical strength. The altered collagen ratio might be the result of the decreased activity of MMP-1, whereas the absent MMP-13 expression did not seem to modify the scar formation. Thus, our data indicate the presence of collagen metabolic disorders in patients with incisional hernias and recurrent incisional hernias. Furthermore, these results might explain the poor results of a mesh-free hernia repair, which again builds up scar tissue of inadequate collagen composition and strength.