  We investigate the asymptotic behavior of solutions of anisotropic equations
of the form
$-\sum_{i=1}^n\partial_{x_i}(\left|\partial_{x_i}u\right|^{p_i-2}\partial_{x_i}u)=f(x,u)$
in $\mathbb{R}^n$, where $p_i>1$ for all $i=1,\dotsc,n$ and $f$ is a
Caratheodory function with critical Sobolev growth. This problem arises in
particular from the study of extremal functions for a class of anisotropic
Sobolev inequalities. We establish decay estimates for the solutions and their
derivatives, and we bring to light a vanishing phenomenon which occurs when the
maximum value of the exponents $p_i$ exceeds a critical value.
