The frequency and temperature dependence of the electronic attenuation of longitudinal ultrasound in indium along [110] has been measured between 1.5 and 4.2 K in the frequency range 10-90 MHz. The zero-field results are well described by a modified free-electron Pippard expression. As expected from general theory the high-field attenuation was proportional to q2 and showed an anisotropy reflecting the symmetry of the electron distribution. The temperature dependence was found to depend on the direction of the magnetic field in the plane normal to q.