The carbon-13 isotropic chemical shifts and anisotropies of the shielding tensors of methyl halides (CH3F, CD3Br, CH3I) and haloforms (CHF3, CDCl3, CDBr3, CHI3) have been determined from carbon N.M.R. spectra in mixtures of liquid crystals with opposite anisotropy of diamagnetic susceptibility. By using these results the components of the chemical shielding tensors were determined. The tensor element σzz(zaxis parallel to theC3symmetry axis) was found to be approximately constant (ca.200 ppm) for methyl halides. The element σxx(= σyy) takes values between 84 ppm (for CH3F) and 226 ppm (for CH3I). On the contrary, the change of σzzfor haloforms was about three times larger than the change of σxx. The experimental shielding tensors of methyl halides have been compared with the theoretical ones calculated by the Coupled Hartree-Fock method. There is a good agreement between the experimental and theoretical values for σzz, but not for σxx. The difference of these values increases when the electronegativity of the substituent decreases, i.e. from F to I.