Abstract: An apparatus monitors a tumble mill and includes at least two vibration sensors mounted on a first main bearing and at least two vibration sensors mounted on a second main bearing of the mill. Sensors may be disposed radially with respect to the bearing. A vibration sensor is also connected to a thrust bearing of the mill oriented in a direction parallel to the rotational axis of the shell of the mill. A signal analyzer receives and analyzes signals from all vibration monitors on the bearings and displays an operating condition of the tumble mill. Additional vibration sensors may be mounted on the shell, and sensors may be provided to sense electrical power input and mechanical power output of the motors. In operation, the mill is loaded with a standard charge and operated at a standard rotational rate. The sensor data is analyzed and displayed when the mill is operating.