The objective of this study was to determine whether hypertension is a risk factor for aneurysm enlargement in patients with an untreated type II endoleak after endovascular abdominal aortic aneurysm repair (EVAR). Between January 2000 and December 2005, 296 patients underwent elective EVAR using a bifurcated Zenith stent graft. Forty-nine (17%) patients had a type II endoleak triaged to observation. Patient clinical data and data on endoleak status, aneurysm size, and endoleak intervention were collected prospectively. Aneurysm size remained the same or decreased in 39 of 49 (80%) patients. In the remaining 10 (20%) patients with aneurysm enlargement, 7 required intervention. There was no difference in initial aneurysm size, patient age, gender, or comorbidities between patients with enlarging aneurysms and those with stable or regressing aneurysms. However, patients with enlarging aneurysms had a mean systolic blood pressure (SBP) of 144 +/- 14 mm Hg compared with 136 +/- 13 mm Hg for patients with stable or regressing aneurysms (p = .08). Multivariate regression analysis demonstrated increased SBP to be an independent predictor of aneurysm enlargement (p = .05). Patients with systolic hypertension and an untreated type II endoleak are more likely to demonstrate aneurysm enlargement after EVAR. Aggressive blood pressure control may be an important adjunct in the management of patients with type II endoleak after EVAR.