The etiology of abdominal aortic aneurysm (AAA) includes inflammation and endothelial dysfunction. To evaluate relations between these mechanisms and AAA growth, endothelin (ET)-1, tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and CD40 ligand were related to yearly AAA growth for 2.9 +/- 1.6 years (mean +/- SD) in 178 patients with conservatively followed AAA. Total number of follow-up years was 491. Abdominal aortic aneurysm diameter increased by 3.3 +/- 4.0 mm during the first year and by 4.9 +/- 4.4 mm during the first 2 years. Median (range) growth was 2.5 (-1.0 to 30.6) mm/year. When patients with AAA growth above or below median were compared, initial AAA diameter (46.1 +/- 5.8 vs 42.0 +/- 8.3 mm; P < .0001), age (75 +/- 7 vs 72 +/- 8 years; P < .029), and initial ET-1 levels (1.31 +/- 0.50 vs 1.13 +/- 0.49 pg/mL; P < .0177) were higher in patients with growth above median. Endothelin 1 (P = .0230) and initial AAA diameter (P = .0019) predicted AAA growth above median in logistic regression. In conclusion, higher initial levels of ET-1 and initial AAA diameter independently predict AAA growth.