Objective: Intimal hyperplasia is a well-known consequence of arterial injury and arterialization in vein grafts. However, the subacute and chronic vein wall changes which occur after catheterization have not been well studied. In this animal study, intimal hyperplasia in the vein wall after catheterization was examined. Methods: A silicon catheter was placed in the anterior caval vein of 54 rats. After in situ fixation at scheduled intervals (1 day to 6 months), the pathologic changes in the vein wall were studied on semi-serial histology sections by means of light microscopy. Results: Three forms of intimal hyperplasia could be observed: plaque-like, papillary-like and incorporation of the mural part of the sleeve into the underlying vein wall. Although the appearance of each was different, their composition was identical. All were mainly composed of α-actin-positive cells and collagen localized above the internal elastin layer, and covered by endothelium if facing the lumen. The plaque-like and papillary-like forms were mainly localized in the anterior vena cava, while sleeve incorporation mainly occurred in the jugular vein. Plaque-like and papillary-like intimal hyperplasia could be seen together on the same slide, but these two forms were never seen together with sleeve incorporation. Conclusion: Intimal hyperplasia occurs after venous catheterization and is probably caused by chronic injury to the vein wall due to knocking and rubbing movements of the catheter against the wall.