Vortices are generated by acoustic oscillations as a second-order viscous effect. Traveling tangential modes in an axially perforated solid propellant rocket give a single vortex swirling about the axis. Tangential velocity at the periphery, typically a few hundred feet per second, can be predicted approximately using acoustic streaming theory modified by heat addition and radial flow effects. Serious consequences of the vortex are 1) torque, which gives undesired roll, especially in large vehicles as torque varies as (radius), and 2) pressure rise caused largely by reduction in the effective area of the nozzle throat. Standing tangential modes produce a pair of vortices rotating in opposite directions for each pressure antinode. These give no net torque and are much less destructive. Experimental data include 3200 frames/ sec cine-films of the vortices, torque measurements, and radial pressure gradient determinations in the head end of a motor. The traveling tangential modes can be initiated readily by tangential injection of nitrogen into the motor.