The vibrational properties of polycrystalline Ln2NiO4+sigma (Ln = La, Pr and Nd) have been investigated by means of Raman scattering in samples with several oxygen contents (delta = 0 and 0.15) at different temperatures (74 K < T < 250 K), and over a spectral range 50-5500 cm-1. The factor group analysis predicts 18 Raman-active modes for the room-temperature phase of stoichiometric samples (delta = 0, orthorhombic D2h18 (Bmab)). Nearly all the observed peaks have been identified with particular atomic displacements even if no selection rules can be applied in powder samples. Two large double-phonon peaks are observed and the dependence of the phonon frequencies on the Ln ion is studied. Two out of the four allowed modes for the oxidized compounds are identified together with some spurious peaks corresponding to defects in the lattice, probably due to randomly distributed interstitial oxygen atoms.