The title compounds, C12H12N6O3S·H2O, (I), and C12H12ClN5OS, (II), are 2-[(4,6-diaminopyrimidin-2-yl)sulfanyl]acetamides. Compound (I) crystallized as a monohydrate. In both compounds, the molecules have a folded conformation, with the pyrimidine ring being inclined to the benzene ring by 56.18 (6)° in (I) and by 67.84 (6)° in (II). In both molecules, there is an intramolecular N—H...N hydrogen bond stabilizing the folded conformation. In (I), there is also a C—H...O intramolecular short contact, and in (II) an intramolecular N—H...Cl hydrogen bond is present. In the crystal of (I), molecules are linked by a series of N—H...O, O—H...O and O—H...N hydrogen bonds, forming undulating sheets parallel to the (100). The sheets are linked via an N—H...Owater hydrogen bond, forming a three-dimensional network. In the crystal of (II), molecules are linked by a series of N—H...O, N—H...N and C—H...O hydrogen bonds, forming slabs parallel to (001).