Viscosities obtained with a falling-body viscometer are reported at pressures up to 300 MPa, over the temperature range 278-353 K, for 1-butyl-3-methylimidazolium acetate ([BMIM][Ac]) samples dried under high vacuum with water content [10(6) x w(H2O) = 258 and 1180] and ion purity x > 0.992. Atmospheric pressure densities are reported for 273-363 K. Comparison is made with literature viscosities and densities at 0.1 MPa. There is a very large variation in the former, which seems in part due to differences in the purities of the source materials. It is recommended that methanol-free reagents should be used for Karl Fischer water analysis of ionic liquid acetates and that samples used for thermophysical property measurements should be well characterized by spectroscopic methods, not just water content. The proton resonance at the C2 position on the imidazolium ring appears to be a good qualitative indication of the dryness. "Activation" volumes, Delta V-double dagger, are calculated from the parameters of a fit to a pressure -modified Vogel Fulcher Tamman (VFT) equation and compared with those for other 1-butyl-3-methylimidazolium ionic liquids. Thermodynamic or density scaling has been applied to the reduced viscosity as a function of the group (TV gamma), gamma being the single scaling parameter, equal to 2.02.