Epidermolysis bullosa (EB) is a genetic condition characterized by skin fragility and blistering. There is no instrument available for clinical outcome research measurements. Our aim was to develop a comprehensive instrument that is easy to use in the context of interventional studies. Item collection was accomplished using a two-step Delphi Internet survey process for practitioners and qualitative content analysis of patient and family interviews. Items were reduced based on frequency and importance using a 4-point Likert scale and were subject to consensus (>80% agreement) using the nominal group technique. Pilot data testing was performed in 21 consecutive patients attending an EB clinic. The final score, Instrument for Scoring Clinical Outcome of Research for Epidermolysis Bullosa (iscorEB), is a combined score that contains clinician items grouped in five domains (skin, mucosa, organ involvement, laboratory abnormalities, and complications and procedures; maximum score 114) and patient-derived items (pain, itch, functional limitations, sleep, mood, and effect on daily and leisurely activities; maximum score 120). Pilot testing revealed that combined (see below) and subscores were able to differentiate between EB subtypes and degrees of clinical severity (EB simplex 21.7 ± 16.5, junctional EB 28.0 ± 20.7, dystrophic EB 57.3 ± 24.6, p = 0.007; mild 17.3 ± 9.6, moderate 41.0 ± 19.4, and severe 64.5 ± 22.6, p < 0.001). There was high correlation between clinician and patient subscores (correlation coefficient = 0.79, p < 0.001). iscorEB seems to be a sensitive tool in differentiating between EB types and across the clinical spectrum of severity. Further validation studies are needed.