Prospective evaluation of 178 radial (RAD) and 114 femoral (FEM) artery catheters inserted in 231 critically ill adults in 2 ICUs was performed. FEM catheter duration (5.8 days) was greater than RAD (3.9 days, p less than .001). Most catheters were removed when no longer needed. Complication rates of RAD (7.5%) and FEM catheters (6.9%) were similar. Digital ischemia was the most common complication (3.5%) yet no digital necrosis occurred. Peripheral vascular disease (PVD), greater age, and greater catheter duration were not associated with more complications. Difficult percutaneous and surgical cutdown insertion of RAD catheters was associated with much greater complication rates. In conclusion, FEM and RAD artery catheters have acceptably low complication rates of 7%. Percutaneous FEM catheterization is recommended as a safe alternative to difficult RAD cannulation.