Proton-catalysed rearrangement of 4,4-dimethyl-5α,13α-androst-7-ene proceeds with methyl migration to give 4,4,14α-trimethyl-18-nor-5α-androst-13(17)-ene. The mechanism of the reaction is discussed in comparison with the rearrangement of various triterpenoids. N.m.r. assignments for C–Me resonances are tabulated.