Symptoms usually present themselves between the ages of 50-70, and include progressive weakness, muscle wasting, and musclefasciculations, spasticity or stiffness in the arms and legs, and overactive tendon reflexes. Patients may present with symptoms as diverse as a dragging foot, unilateral muscle wasting in the hands, or slurred speech.

Neurological examination presents specific signs associated with upper and lower motor neurone degeneration. Signs of upper motor neurone damage include spasticity, brisk reflexes and the Babinski sign. Signs of lower motor neurone damage include weakness and muscle atrophy.

Note that every muscle group in the body requires both upper and lower motor neurones to function. The signs described above can occur in any muscle group, including the arms, legs, torso, and bulbar region.

The symptoms described above may resemble a number of other rare diseases, known as "MND Mimic Disorders". These include, but are not limited to, multifocal motor neuropathy, Kennedy's disease, hereditary spastic paraplegia, spinal muscular atrophy and monomelic amyotrophy. A small subset of familial MND cases occur in children, such as "juvenile ALS", Madras syndrome, and individuals who have inherited the ALS2 gene. However, these are not typically referred to as MND, but by their specific names.