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La2Ni04. q25 exhibits a cooperative ordering of dopant-induced holes and Ni spins below a transition temperature of 110 K. There is also an ordering of interstitial oxygens that occurs near room temperature. We present a comprehensive analysis of experimentally observed superlattice intensities in terms of structural models, justifying previous identifications. The model for the interstitial order involves a 3a x 5b x 5c unit cell with an ideal interstitial density of b = -per formula unit.In the spin and charge ordered state, the magnetic moments are sinusoidally modulated within the Ni02 planes. The moments point transverse to the modulation direction, with nearest neighbors antiparallel, and have a maximum amplitude that is ) 80'Fp of that observed in undoped LaqNi04.A corresponding modulation of atomic positions within Ni02 planes involves breathing-mode distortions consistent with a modulation of the charge density. The results are compared with theoretical models and with experimental observations on related systems.