Various criteria are known for assuring uniqueness of the solution of a system ofn ordinary differential equations,x′ = f(t, x), with initial conditionx(t0) = x0. Most of these involve some sort of relaxed Lipschitz condition onf(t, x), with respect tox, valid on an open setD ⊂ R1+n which contains the point (t0, x0). The present paper generalizes (and unifies) a number of known uniqueness criteria to cover cases when (t0, x0) lies on the boundary ofD.