A first measurement is presented of exclusive photoproduction of ρ 0 mesons associated with leading neutrons at HERA. The data were taken with the H1 detector in the years 2006 and 2007 at a centre-of-mass energy of √s = 319 GeV and correspond to an integrated luminosity of 1.16pb−1 . The ρ 0 mesons with transverse momenta p T L > 0.35, are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality Q2 , the total energy of the photon-proton system 20 0 nπ + is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a ρ 0 meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, σel (γπ+ → ρ°π + ), is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction γ p → ρ°nπ + .