The formation of porous on tantalum was investigated in electrolytes containing low concentrations of HF (0.15 wt %). Under optimized electrochemical conditions, porous consisting of self-assembled pore arrays with single pore diameters of and a pore spacing of forms. The pore structure and the pore distribution depend on the concentration of HF, the anodization voltage, and the time for anodic oxidation. Porous layers thick with a regular pore distribution can be formed. For thicker layers cracking and a tendency for delamination was observed. © 2005 The Electrochemical Society. All rights reserved.