Rotational transitions of (NeH+)-Ne-20, (NeD+)-Ne-20, (NeH+)-Ne-22, and (NeD+)-Ne-22 were observed in the 1-5 THz frequency region with a high-precision far-infrared spectrometer using a tunable radiation source. Observed frequencies were incorporated with previous infrared measurement to redetermine Dunham coefficients Y-kl and isotopically independent parameters U-kl, Delta(kl)(H), and Delta(kl)(Ne), where Delta(02)(H) and Delta(01)(Ne) were determined for the first time.