The author studies the nonlinear boundary value problem consisting of the equation \(u''+ a(t)f(u)= 0\) with the boundary conditions \(\alpha u(0)- \beta u'(0)= 0\), \(\gamma u(1)+\delta u'(1)= 0\), where \(a\) is allowed to be unbounded near the endpoints \(t= 0\) and \(t=1\), and \(f\) is either superlinear or sublinear. By applying a fixed point theorem, the author proves the existence of at least one positive solution to the problem. This result is a development of the recent work on nonlinear boundary value problems by Erbe and Wang, and by Zhang.