Tandem gait is a gait (method of walking) with very small steps in a straight line so that, with each step, the heel of the foot that steps forward is placed immediately in front of, or just touching, the toes of the rear/supporting foot.

Neurologists sometimes ask patients to walk in a straight line using tandem gait as a test to help diagnose ataxia, especially truncal ataxia, because sufferers of these disorders will have an unsteady gait. Walking in tandem magnifies the unsteadiness. However, the results are not definitive, because many disorders or problems can cause unsteady gait (such as vision difficulties, problems with the motor neurons, associative cortex or weakness of the lower limbs due to non-neurological causes). Therefore, inability to walk correctly in tandem gait does not prove the presence of ataxia.^{[citation needed]}

Profoundly affected tandem gait with no other perceptible deficits is a defining feature of posterior vermal split syndrome.^[1]

Suspects may also be asked to perform a tandem gait walk during the "walk and turn" part of a field sobriety test.^[2]