Motor Neuron disease presents with muscular atrophy, increased reflexes, spasticity, fasciculations, tongue atrophy, swallowing difficulties and problems in speech. Mult ıfactorial causes are mentioned in etiology but exact cause is unknown. In this report, we present a 59-year-old male patient who applied with psychiatric symptoms including personality changes and lability of mood. Further investigations revealed a motor neuron disease. A year ago, the symptoms of inappropriate laughing and crying, frequent nail cut, speedy and careless driving, nervousness and sadness had begun abrubtly. In electromyography (EMG), neuronal conduction was within normal ranges, but in needle EMG frequent fasciculations and high amplitude polyphasic motor unit potentials (MUP) were observed in both upper and lower extremities. According to the neurologic exam and laboratory findings the patient was diagnosed as motor neuron disease. Since fluoxetine was known to be effective in similar cases, 20 mg per day was giyen. This rase report mentions the motor neuron disease's possible psychiatric symptoms and emphasizes the beneficial role of fluoxetine in the treatment.