The room‐temperature attenuation for longitudinal acoustic waves propagating in thecdirection in high‐purity CdS has been measured from 0.1 to 0.6 GHz. At 0.5 GHz the attenuation is 46 dB/cm (tan&dgr;=0.0015). From the observed attenuation corrected for phonon‐electron contributions and a lattice loss theory of Woodruff and Ehrenreich, a Gru¨neisen parameter of ± 1.51 is calculated. An alternate method of calculating the Gru¨neisen parameter by using the pressure dependence of the elastic constants gives a Gru¨neisen parameter of ‐1.37.