Synthesis, crystal structures and IR spectra of the first representatives of calcium hydrogen selenite halides are reported. Colourless prismatic crystals of calcium hydrogen selenite chloride Ca(HSeO3)Cl and corresponding hydrated analogue Ca(HSeO3)Cl(H2O) were produced upon evaporation of aqueous solutions. Ca(HSeO3)Cl is monoclinic, P21/c, a = 7.0031(11) Å, b = 7.7336(12) Å, c = 8.5024(13) Å, β = 109.889(3)°, V = 433.02(12) Å3, R1 = 0.039. Ca(HSeO3)Cl(H2O) is orthorhombic, Pbca, a = 6.222(4) Å, b = 10.413(7) Å, c = 16.875(10) Å, V = 1093.3 (12) Å3, R1 = 0.041. Ca(HSeO3)Cl and Ca(HSeO3)Cl(H2O) represent new structure types. In both structures, Ca2+ cations adopt mixed-ligand environments formed by oxygen atoms of hydrogen selenite anions (and water molecules for Ca(HSeO3)Cl(H2O)) and chloride ions. Both structures are layered. The crystal structure of Ca(HSeO3)Cl(H2O) demonstrates a rare phenomenon of hydrogen-bonded assembly of water and chloride in the interlayer space.