Alumina whiskers have been grown on single‐crystal alumina substrates by heating aluminum filings, located near the crystals, to 1400°C in a stream of wet hydrogen. The whiskers grew crystallographically coherent with the substrate, and had their axes either parallel to thecaxis or in one of 12 equally spaced directions in the basal plane. These 12 directions divide into two distinct sets, a ⟨112¯0⟩ set and a ⟨11¯00⟩ set, each having sixfold symmetry, and with the directions of one set midway between the directions of the other. These growth directions are the screw‐dislocation directions in alumina, hence it seems plausible that the whiskers grew coherently with the substrate at the site of emergent screw dislocations.