Fixed drug eruption (FDE) is defined as sharply demarcated erythematous patches or plaques that occur secondary to systemic exposure to a causative medication. Eruptions are deemed "fixed" because upon repeated exposure they recur at previously affected sites. Generalized bullous fixed drug eruption (GBFDE) is a rare FDE variant occurring in patients with a previous history of FDE. Given the extensive cutaneous involvement and the frequent mucosal ulcerations associated with GBFDE, it is challenging to discern these lesions from Steven-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). The presence of significantly elevated lesional and serum granulysin in SJS/TEN is an important discriminating factor because granulysin levels remain significantly lower in GBFDE. The implementation of an immunochromatographic test for rapid detection of elevated granulysin levels could therefore facilitate the early diagnosis of SJS/TEN. We report a case of GBFDE to elucidate the characteristic differences in clinical presentation, histopathology, and immunohistochemistry that can facilitate diagnosis.