Let
H
(
n
)
\mathcal {H}(n)
be the maximum number of limit cycles that a planar polynomial vector field of degree
n
n
can have. In this paper we prove that
H
(
n
)
\mathcal {H}(n)
is realizable by structurally stable vector fields with only hyperbolic limit cycles and that it is a strictly increasing function whenever it is finite.