The asymmetric unit of the title compound, NH4 +·C11H14N6O7P-·0.5H2O, contains one 3′-azido-3′-deoxythymidine-5′aminocarbonylphosphonate (ACP-AZT) anion, half of an NH4 + cation lying on a twofold rotation axis and in another position, occupied with equal probabilities of 0.5, an NH4 + cation and a water molecule. The amide group of the ACP-AZT anion is disordered (occupancy ratio 0.5:0.5), with one part forming an N - H⋯O (involving C=O⋯H4N+) hydrogen bond and the other an O - H⋯N (involving C - NH2⋯OH2) hydrogen bond with the components of the split NH4 +/H2O position. The pseudorotation parameters of ACP-AZT set it apart from previously studied AZT and thymidine. In the crystal, the various components are linked by N - H⋯O, O - H⋯O, N - H⋯N, C - H⋯O and C - H⋯N hydrogen bonds, forming a three-dimensional framework.