The formation of salts in the l-cysteine–HNO3–H2O system was studied yielding three representatives as single crystals: anhydrous l-cysteinium nitrate (l-CysH)NO3 (I) and two new salts (l-CysH···l-Cys)NO3 (II) and (l-CysH···l-Cys)NO3∙0.5H2O (III) with the dimeric (l-CysH···l-Cys) cation. (I), (II) and (III) crystallize in space groups P212121, P21 and I2, respectively. Dimeric cations in (II) and (III) were formed by very short O–H···O hydrogen bonds with R(O···O) distances of 2.440(2) Å and 2.4352(17) Å, respectively. Infrared and Raman spectra of (I-III) were registered and discussed in relation to crystal structures. Characteristics of dimeric cations are compared with those in the previously obtained compounds of l-CysH(l-CysH···l-Cys)F(F···HF), (l-CysH···l-Cys)Cl, (l-CysH···l-Cys)Br and (l-CysH···l-Cys)I·0.5H2O.