The aim of this article is twofold: to provide asymptotic behavior and error estimates results for an elliptic dimension reduction problem. The problem is posed in a bounded and thin domain
,
where
when
(the thickness of
is of order
while its diameter is of order 1). The limit problem is elliptic and is posed in
. Under the assumptions that
has a smooth boundary
and homogeneous Dirichlet boundary condition, we give two important results, first an estimate of the global error (of order
), and then an estimate of the
global and
interior errors (of order
).