We answer a question posed by Mordell in 1953, in the case of repeated radical extensions, and find necessary and sufficient conditions for
$[F[\sqrt [m_1]{N_1},\dots ,\sqrt [m_\ell ]{N_\ell }]:F]=m_1\cdots m_\ell $
, where F is an arbitrary field of characteristic not dividing any
$m_i$
.