Objectives. This study assessed the relation between histologic acute and long-term lumen size after coronary angioplasty. Background. Angiographic studies suggest that the creation of a larger acute lmmen is associated with a reduced incidence of restenosis. Histologic evaluation of the influence of the acute lumen on late outcome has not been previously reported. Methods. Detailed histologic examination and planimetry were performed in 28 postmortem coronary arteries subjected to angioplasty at an average of 71 weeks antemortem. The lumen area on each histologic segment was defined as the final lumen area. The lumen area immediately after angioplasty, the acute lumen area, was deined by the sum of the neointimal area plus final lumen. A final lumen area ≥ 25% of the arterial area was considered a long-term success; a final lumen area < 25% was considered a long-term failure. Results. Arterial size and neointimal area were similar in long-term successes aid failures. In successes, the mean (±SD) acute lumen area was greater than in failures (4.1 ± 1.9 vs. 2.7 ± 1.4 mm2, respectively, p < 0.001). The acute lumen area as a percent of arterial area was 46 ± 10% in successes versus 27 ± 11% in failures (p < 0.0001). The corresponding estimated mean acute lumen diameter stenosis was 24 ± 8% in successes versus 42 ± 12% in failures (p < 0.0001). Plaque area was greater in failures (7.1 ± 3.2 mm2) than in successes (4.8 ± 2.4 mm2, p < 0.002). Conclusions. Neointimal proliferation after angioplasty occurs in all dilated coronary arteries, and the amount of neointimal growth is independent of vessel size. The creation of a larger lumen and a larger lumen as a percent of vessel size were associated with an improved long-term histologic patency. © 1994.