More than 100 calculations of vibrational frequencies for cis-[Pt(NH3)2X2] (X = Cl-, Br-) and trans-[Pt(NH3)2Cl2] have been published over the past 25 years. The high-quality Raman spectra presented here have sufficient resolution in the crucial region of metal-ligand modes to permit an assessment of frequency calculations. The peaks for symmetric and antisymmetric Pt-Cl stretching modes νs and νa are resolved in the 312-333 cm-1 region. Frequency variations due to 35Cl and 37Cl isotopes are shown to be comparable in size to the differences between νs and νa. Peaks corresponding to the two Pt-Br stretching frequencies are observed at 213 and 218 cm-1 and Pt-N stretching frequencies for all compounds between 485 and 540 cm-1. The crystal structures of trans-[Pt(NH3)2Cl2] and cis-[Pt(NH3)2Br2] at 300 and 120 K are reported and complement the variable-temperature vibrational frequencies.