The problem of a penny-shaped crack propagating in an unbounded isotropic linear elastic body is solved. The crack expands from a zero radius in a self-similar manner and is assumed to have speed larger than the S-wave speed and less than the P-wave speed. A tensile load is directed normal to the crack at infinity. The method of self-similar potentials and rotational superposition are applied. Attention is given to the stress singularity at the crack border.