  We investigate monotone idempotent $n$-ary semigroups. One of the main result
of this article is the generalisation of Czogala-Drewniak Theorem, which
describes the idempotent monotone associative functions having neutral element.
Furthermore we present the full characterisation of idempotent, monotone,
$n$-associative functions on an interval which have neutral elements. %{\bl
defined}. Our description provides that monotone, idempotent, $n$-ary
semigroups are quasitrivial.
