The structure and vibrational spectrum of cis-Rh(NH 3 )(CO) 2 Cl has been computed using DFT/B-LYP with 6-311G ∗∗ for all except the rhodium atom. For this a 6s5p3d basis with an electron core potential was employed. The predicted skeletal structure is in good agreement with reported experimental values of similar rhodium(I) compounds. The computed vibrational frequencies agree well with experimental IR data for cis-Rh(NH 3 )(CO) 2 Cl and its ND 3 , 15NH3 and 13 CO isotopomers. Some of the earlier vibrational assignments are revised and the molecular force field established. The structural agostic effect is discussed and compared to that in other rhodium compounds.