The reemitted positron yield from a 1500-A-thick Ni(100) foil was measured as a function of incident positron energy. The magnitude of the positron internal surface reflection coefficient, {ital scrR}=0.63{plus minus}0.04, was determined by fitting calculated positron yields to the data. This value agrees with the value calculated using the one-dimensional, potential-step model advanced by Britton {ital et} {ital al}. (Phys. Rev. Lett. 62, 2413 (1989)). The mean positron penetration depth varies with incident positron energy as {ital {bar z}}={alpha}{ital E}{sup {ital n}}, where {alpha} is fixed ({alpha}=400/{rho} A/keV{sup {ital n}}, {rho} is the sample density in g cm{sup {minus}3}) and {ital n}=1.61{plus minus}0.03, in good agreement with positron back-reemission measurements from thick single crystals.