Key words Functional differential equation with advanced arguments, periodic boundary value problem, comparison results, uniqueness of solution MSC (2000) 34K10, 34K12, 34A40, 34B15We prove some comparison results for the periodic boundary value problem related to a first-order functional differential equation of advanced type. These maximum principles provide uniqueness results for nonlinear differential equations with advanced arguments. By a change of variable, we deduce analogous results for fuctional differential equations with delayed arguments.