We study a comparison principle and uniqueness of positive solutions forthe homogeneous Dirichlet boundary value problem associated to quasi-linear elliptic equations withlower order terms. A model example is given by
$ -\Delta u+\lambda\frac{|\nabla u|^2}{u^r} = f(x), \qquad\lambda,r>0.$
The main feature of these equations consists in having a quadratic gradient term in which singularities are allowed. The arguments employed here also work to deal with equations having lack of ellipticity or some dependence on u in the right handside. Furthermore, they could be applied to obtain uniqueness results for nonlinear equations having the p-Laplacian operator as the principalpart. Our results improve those already known, even if the gradient term is not singular.