Background: Hidradenitis suppurativa (HS) is a chronic, inflammatory and recurrent skin disease. Different staging instruments have been suggested, but none has achieved universal acceptance. Despite the fact that Hurley staging is one of the most widely applied HS disease severity staging instruments, it has not been validated. Objectives: To determine the inter- and intrarater reliability of the Hurley staging system. Methods: Fifteen raters (five plastic surgeons, five general surgeons and five dermatologists) independently staged 30 photos of patients with HS according to Hurley staging at two time points. Reliability was assessed using kappa (&kgr;) statistics, and multivariable logistic regressions were used to determine independent risk factors for photos with discordant staging. Results: Inter-rater reliability was moderate for the three stages of HS [κ = 0·59, 95% confidence interval (CI) 0·48–0·70]. It was moderate for Hurley stage I (κ = 0·45, 95% CI 0·32–0·55) and stage II (κ = 0·51, 95% CI 0·31–0·71) and it was almost perfect for stage III (κ = 0·81, 95% CI 0·62–1·00). The intrarater reliability was substantial for all stages and all raters (κ = 0·65, 95% CI 0·58–0·72). For stage I it was moderate (κ = 0·50, 95% CI 0·38–0·62), for stage II it was substantial (κ = 0·62, 95% CI 0·51–0·73) and for stage III it was almost perfect (κ = 0·82, 95% CI 0·77–0·87). Hurley stages II and III were less likely to result in discordant staging than Hurley stage I (odds ratios 0·47, 95% CI 0·29–0·77 and 0·21, 95% CI 0·12–0·38, respectively). The mean time spent on staging a photo was 14 s. Conclusions: Hurley staging is reliable for rapid severity assessment of HS, with moderate inter-rater and substantial intrarater reliability for all stages. It is best for assessing Hurley stage III HS, which is an indication for surgery.