Purpose: To compare the outcome of endovascular aneurysm repair (EVAR) versus conventional open repair (OR) in patients with a short, angulated or otherwise challenging proximal neck. Methods: The definition of a challenging proximal neck was based on diameter (>= 28 mm), length (<= 115 mm), angulation (>= 60 degrees), shape (reverse tapered or bulging), and thrombus lining (>50%). Between January 2005 and December 2007, 187 consecutive patients (159 men; mean age 73 years, range 48-92) operated for asymptomatic abdominal aortic aneurysm (AAA) were identified as having challenging proximal neck morphology. Of these, 61 patients were treated with OR at center I (group A), 71 with standard EVAR (group B; 45 center I, 29 center II) and 52 with fenestrated EVAR (group C) at center II. Clinical examination and computed tomography were performed at 1 month and yearly thereafter. Results: There was no statistically significant difference between groups A, B, and C regarding primary technical success rate, 30-day mortality, or late AAA-related mortality. The mean length of follow-up was 19.5 months (range 0-40). Freedom from reintervention at 3 years was 91.8%, 79.7%, and 82.7% for groups A, B, and C, respectively (p=0.042). The only statistically significant difference between standard and fenestrated EVAR was a higher incidence of late sac expansion [9 (12.2%) versus 1 (1.9%), p=0.036] in the standard stent-graft group. Reinterventions were more frequent after EVAR (p=NS), but open reinterventions were more common after OR. Reinterventions after EVAR were related to the presence of an angulated (p=0.039) or short neck (p=0.024). Conclusion:The results of EVAR and OR were similar for AAAs with a challenging proximal neck. Endovascular reinterventions were more frequent after EVAR, particularly in patients with an angulated or short neck. Open reinterventions were more common after OR. More patients and long-term data are needed to confirm these findings. J Endovasc Ther. 2009;16:137-146