Electronic Journal of Differential Equations, Vol. 2011 (2011), No. 118, pp. 1-5. Title: Existence and uniqueness of solutions for a Neumann boundary-value problem Authors: Safia Benmansour (Univ. Abou Bekr Belkaid, Tlemcen, Algerie) Mohammed Bouchekif (Univ. Abou Bekr Belkaid, Tlemcen, Algerie) Abstract: In this article, we show the existence and uniqueness of positive solutions for perturbed Neumann boundary-value problems of second-order differential equations. We use a fixed point theorem for general $\alpha$-concave operators. Submitted July 25, 2011. Published September 14, 2011. Math Subject Classifications: 34B15, 47N20. Key Words: Positive solution; existence and uniqueness; normal cone; $\alpha$-concave operator; Green's function.