Pathologic laughter and crying (PLC) is the involuntary occurrence of laughter and crying in the absence of a corresponding change in affect. PLC resulting from structural brain damage in patients with traumatic brain injury can be the cause of substantial social dysfunction in these patients. The use of lamotrigine as an antiepileptic drug and mood stabilizer is well established; its use in PLC has been reported only once during treatment following a stroke. We present here four young patients with pathological laughter and/or pathological crying following traumatic brain injury who were successfully treated with lamotrigine. Data supporting the use of lamotrigine in the treatment of PLC following traumatic brain injury and the neuroanatomy of pathological laughing are briefly reviewed.