Abstract The crystal structure of 1-(2-thiazolylazo)-2-naphthol, C13H9N3OS, has been determined from three-dimensional X-ray data collected by counter methods. The crystals are monoclinic with space group P21/a; cell dimensions: a=17.721(1), b=28.366(2), c=4.699(1) Å, β=91.78(1)°, and Z=8. The structure was solved by the symbolic addition procedure and refined by the least-squares method to give an R value of 0.051 for 2150 observed reflections. There are two crystallographically independent molecules in an asymmetric unit; both of the molecules show a generally similar shape and size, but their structural details differ in planarity and distribution of the bond lengths. Both molecules have the azo and hydrazone character, but the equilibrium is shifted toward the azo tautomer.