Electronic Journal of Differential Equations, Vol. 2011 (2011), No. 51, pp. 1-19. Title: Second-order boundary estimates for solutions to singular elliptic equations in borderline cases Authors: Claudia Anedda (Univ. di Cagliari, Italy) Giovanni Porru (Univ. di Cagliari, Italy) Abstract: Let $\Omega\subset R^N$ be a bounded smooth domain. We investigate the effect of the mean curvature of the boundary $\partial\Omega$ on the behaviour of the solution to the homogeneous Dirichlet boundary value problem for the equation $\Delta u+f(u)=0$. Under appropriate growth conditions on $f(t)$ as $t$ approaches zero, we find asymptotic expansions up to the second order of the solution in terms of the distance from $x$ to the boundary $\partial\Omega$. Submitted January 10, 2011. Published April 13, 2011. Math Subject Classifications: 35B40, 35J67. Key Words: Elliptic problems; singular equations; second order boundary approximation.