We report measurements of the critical exponents β, γ, ν and their amplitude coefficients for the order-disorder phase transition at a clean metal surface, the Au(110) (1 × 2)↔(1 × 1) transition. Experiments were conducted with a new high resolution LEED method. The results show that the phase transition is strictly two-dimensional, belonging to the Ising universality class. We clearly detect the critical scattering peaking aboveTc, signaling the breakdown of the Ornstein-Zernike theory.