The asymmetric unit of the title compound, poly[(μ4-{[bis(hydrogen phosphonatomethyl)azaniumyl]methyl}phosphonato)lanthanum(III)], [La(C3H9NO9P3)]n, comprises an La3+ center and a H3nmp3− anion (where H3nmp3− is a residue of partially deprotonated nitrilotris(methylenephosphonic acid), namely {[bis(hydrogen phosphonatomethyl)azaniumyl]methyl}phosphonate). This study concerns a structural redetermination using single-crystal X-ray diffraction data, collected at the low temperature of 180 K, of a recently investigated material whose structural details have been proposed from powder X-ray diffraction studies [Silva et al. (2011 ▶). J. Am. Chem. Soc. 133, 15120–15138]. The main difference between the two models rests on the position of the H atoms. While two H atoms were modeled as attached to the same phosphonate group in the powder determination, in the current model, the same H atoms are instead distributed among two of these groups. The sample studied was an inversion twin.