Efficient non-destructive fault detection and severity assessment can be performed using vibration analysis. This paper studies gear tooth crack detection through investigating the natural frequencies of the studied gear model. The gear mesh stiffness was obtained analytically, and dynamic simulation was performed. Moreover, the frequency response functions (FRFs) were calculated for healthy and faulty gears. A change in the eigenfrequencies could be observed with increasing crack size, and thus the dynamic response could give an indication of gear tooth cracks.