We investigated smooth muscle cell proliferation associated with restenosis after percutaneous transluminal coronary angioplasty (PTCA) in 8 arteries with fragmented internal elastic lamina obtained at autopsy in 7 patients who died between 2 months to 2 years 11 months after coronary angioplasty. The internal elastic lamina fragmentation, measured longitudinally along the blood vessels, measured 6.6 +/- 6.9 mm. Smooth muscle cell proliferation was concentrated around the fragmented internal elastic lamina, extending longitudinally even to unfragmented areas. The proliferation of smooth muscle cells extended for 1.8 +/- 2.2 mm in the proximal portion of the fragmentation, and for 2.0 +/- 2.9 mm in the distal portion. The possibility of new stenoses resulting from smooth muscle cell proliferation at sites adjacent to those subjected to PTCA should be borne in mind when PTCA of the proximal segments of the left anterior descending coronary artery is contemplated.