Platinum films have been deposited by dc sputtering in an argon discharge, using plane parallel electrodes. The system was used either for diode sputtering or, by addition of a heated filament, for triode sputtering with the same geometry. Both configurations were used to maintain constant discharge current and voltage over the pressure range 10–150 mTorr. Films were deposited over this pressure range for sputtering voltages between 1.5 and 4.0 kV. The mass deposited in a given time decreased with increasing pressure and decreasing voltage. Films up to 0.7 μ thick were deposited, and the film density decreased linearly from near the bulk value to 60% of the bulk value as the pressure increased from 10 to 150 mTorr. At the same time, the resistivity increased from twice the bulk value to ten times the bulk value while the temperature coefficient of resistance was between 30%–50% of the bulk value. For the densest films, the product of resistivity and temperature coefficient was close to the value predicted by Matthiessen's rule for platinum. Since no significant doping of the platinum was observed, the change in electrical properties is attributed to porosity in the films. The crystal structure was examined both by x-ray diffractometer and wide-film Debye-Scherrer techniques. As the resistivity increased, the crystalline orientation in the films became more random and the grain size decreased although the crystal structure of bulk platinum was maintained. It is suggested that the porosity is due to decreasing surface mobility caused by the increasing pressure and that this may be inherent in the sputtering process so that all films sputtered at pressures above approximately 20 mTorr may have some porosity.