AbstractPatients with psoriasis vulgaris have a higher incidence of pemphigoid than the general population. However, there are only a few concise reports on the coexistence of generalized pustular psoriasis (GPP) and pemphigoid. The authors describe a rare case of the simultaneous development of GPP and pemphigoid with multiple autoantibodies (i.e., BP180–C‐terminal, 200‐kDa protein, and laminin 332 proteins) in a complete responder of immune checkpoint inhibitor (ICI) treatment for lung cancer. Anti–interleukin 17 inhibitors for the GPP and oral corticosteroids at 10 mg/day for the pemphigoid effectively achieved remission in both diseases. It may not be uncommon to detect multiple autoantibodies in patients with pemphigoid; however, the detection of autoantibodies to more than three antigens in a single patient is relatively rare. In the current patient, the severe inflammation of GPP might have generated multiple autoantibodies. In addition, although pembrolizumab achieved a complete response and was discontinued 9 months before the onset of GPP and pemphigoid, the ICI might have affected the development of the two diseases. This case report adds useful information to the limited knowledge regarding the coexistence of GPP and pemphigoid, and aids in a better understanding of the pathological mechanisms and treatment options for such patients. Furthermore, the possibility that more patients may develop multiple autoimmune and autoinflammatory diseases in the era of ICIs should be recognized.