In the inherited blistering skin disease, recessive dystrophic epidermolysis bullosa (RDEB), there is clinical heterogeneity with variable scarring and susceptibility to malignancy. Currently, however, there are few biochemical markers of tissue inflammation or disease progression. We assessed whether the non‐histone nuclear protein, high mobility group box 1 (HMGB1), which is released from necrotic cells (including keratinocytes in blister roofs), might be elevated in RDEB and whether this correlates with disease severity. We measured serum HMGB1 by ELISA in 26 RDEB individuals (median 21.0 ng/ml, range 3.6–54.9 ng/ml) and 23 healthy controls (median 3.6, range 3.4–5.9 ng/ml) and scored RDEB severity using the Birmingham Epidermolysis Bullosa Severity Score (BEBSS; mean 34/100, range 8–82). There was a positive relationship between the BEBSS and HMGB1 levels (r = 0.54, P = 0.004). This study indicates that serum HMGB1 levels may represent a new biomarker reflecting disease severity in RDEB.