Background and Objetives: Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are considered as a continuum of the same process. TEN or Lyell Syndrome is the most severe form. Both entities involve an acute mucocutaneous blistering reaction associated with systemic inflammation. Materials and Methods: We present a case of a young woman who developed TEN following concomitant treatment with valproate, lamotrigine, and phenobarbital. Despite the extensive mucocutaneous detachment (over 90%), prognostic evaluation was favorable (SCORTEN score 2; probability of survival 88%), and this patient evolved satisfactorily. Five days after admission, valproate was reinitiated without any subsequent adverse reaction. Results: Causality evaluation identified both lamotrigine and phenobarbital as “very probable” (ALDEN score = 6) causes and valproate as “very unlikely” (ALDEN score = 0) cause of TEN. Conclusions: SJS and TEN are true life-threatening medical emergencies. This case emphasizes the importance of early diagnosis and treatment, including the discontinuation of the causative agent, which can be lifesaving.