Generalized pustular psoriasis (GPP) is a rare neutrophilic skin condition characterized by episodes of widespread eruption of sterile macroscopic pustules that can be associated with systemic inflammation. The rarity of GPP and its heterogeneous cutaneous and extracutaneous symptoms pose considerable challenges to the development and adoption of comprehensive accurate disease measures for the routine clinical assessment of disease severity and the evaluation of new treatments in clinical trials. Psoriasis disease measures remain among the most commonly used methods for evaluating patients with GPP, despite their limitations owing to a lack of assessment of pustules (a hallmark of GPP), systemic inflammation, and disease symptoms. The adaptation of psoriasis disease measures and the development of assessment tools specific for GPP severity will enable more effective and accurate monitoring of patients with GPP and enhance the clinical development of new therapies. Further clinical validation of recently developed modified assessment tools, such as the Generalized Pustular Psoriasis Physician Global Assessment and the Generalized Pustular Psoriasis Area and Severity Index, and international consensus on using quantitative tools and patient-reported outcome measures in the development of new treatments are needed to advance patient care. Graphic abstract: [Figure not available: see fulltext.].