X-Ray Diffraction, Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy studies have been made of TlInS2 layered semiconductor compound to clarify its crystal structure, which has remained ambiguous through several decades. Similarly, in recent studies it has been reported at ambient conditions this semiconductor can crystallize in several polytypes with monoclinic structure, which may be present in the same sample. In this study it was found at ambient temperature TlInS2 crystallized in a monoclinic structure, space group C2/c with lattice parameters a = 8.609 Å, b = 14.904 Å, c = 9.471 Å, ß = 110.44 °, it was not found the presence of more than one polytype in the studied sample. Additionally, the results obtained were compared with other previously derived using an analysis of the vibration modes of the compound by means of Raman spectroscopy. [ABSTRACT FROM AUTHOR]