N-Acyl-N′-phenylhydrazines rearrange under basic conditions to afford o-aminophenyl- acetamides. This reaction can be rationalized in terms of [3, 3] sigmatropic shifts of enolized intermediates. The Sommelet-Hauser-type and Stevens-type rearrangements of both aromatic and aliphatic acylhydrazines compete with the [3, 3] rearrangement.