Several 2-hydroximino-1,3-thiazolidine-4-ones have been prepared by reaction of the respective α-thiocyanatocarbonic acid esters with hydroxylamine. They have been characterized by ir, uv and 1H-nmr. The chemical structure was determined unequivocally by the crystal structure analysis of 5-ethyl-2-hydroximino-1,3-thiazolidine-4-one, space-group: P21/c, a = 10.0382(7), b = 5.2903(4), c = 19.305(1) Å, β = 134.233(4) at T = 24(1)°C. The structural model was refined with 3196 data to give R = 0.044. Analysis of the bonding geometry has lead to characterization of the 2-amino-1,3-thiazolidine-4-ones as cyclic N-thiaiminoamides.