The thiospinels of composition FeCr(2)S(4) and Fe(1+x)Cr(2-2x)Sn(x)S(4) with 0<x<0.1 have been examined by means of extended x-ray absorption fine structure, Mössbauer spectroscopy and magnetoresistance techniques. The structural characterization shows that tin enters the spinel-related lattice as Sn(4+) and occupies the octahedral B site. Appreciable magnetoresistance is observed in the temperature range 160-185 K which includes the magnetic ordering temperature. The effect of slight non-stoichiometry in FeCr(2)S(4) and of tin doping is observed in the Mössbauer spectra which show the Fe(2+) ions to occupy the tetrahedral A sites. The Mössbauer spectra recorded around the magnetic ordering temperature are sensitive to small (0.03 T) applied magnetic fields. The influence of tin on the low temperature magnetic behaviour is associated with the distribution of Cr(3+), Sn(4+) and Fe(3+) ions around tetrahedral Fe(2+) sites and vacancies in the anionic sublattice. An interpretation of the colossal magnetoresistance phenomena below T(N) is suggested.