Scanning tunneling microscopy has been used to characterize the initial stages of epitaxial growth of HfB2 on a Hf(0001) surface. The film was grown on the substrate at 780 degreesC through chemical vapor deposition using diborane gas. The growth mechanism appears to combine 2D layer by layer growth with 3D island formation. The HfB2 film first appears as multilayered islands on top of large unreacted Hf(0001) terraces with the island edges aligned with the substrate step ledges. For thicker films only hexagonally shaped multilayered HfB2 islands with an average size of 100 Angstrom are seen.