The magnetic order and critical behavior of well-defined (100)p(1×1) surfaces of ultrathin (1–7 monolayers) vanadium films deposited on atomically clean and flat Ag(100) substrates is studied by electron capture spectroscopy, a novel method which probes electron spin polarization (ESP) at the topmost surface. For all investigated films, the long-ranged ESP is nonzero, demonstrating the existence of long-ranged ferromagnetic order at the film surface. For a 5-monolayer-thick film, ferromagnetic order sets in at a critical surface temperature TCs=475.1 K. In the temperature range from 200 to 475.1 K, the ESP of the topmost surface layer follows the power law (TCs−T)β, with β=0.128±0.01. This result is in good agreement with the exact value β= (1)/(8) of the two-dimensional Ising model.