The cross section for the diffractive deep-inelastic scattering process ep -} eXp is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data sample covers the range x(P) { 0.1 in fractional proton longitudinal momentum loss, 0.1 { vertical bar t vertical bar { 0.7 GeV(2) in squared four-momentum transfer at the proton vertex and 4 { Q(2) { 700 GeV(2) in photon virtuality.