Abstract In the present paper we calculate the magnetic hyperfine coupling constants (hfcc) α iso and A ij of the ground states of the isotopes NH 2, NHD and ND 2 using truncated MR-CI methods. Differences from other theoretical methods and shortcomings of the truncated CI approach in calculating α iso are studied. Polarization effects with determine α iso, as well as a simple model to describe the dipolar hfcc's, are discussed. All results are in excellent agreement with experimental data. It is shown that ab initio methods are able to obtain reliable values for off-diagonal values of A ij which are difficult to measure experimentally.