Background Hidradenitis suppurativa (HS) is a chronic recurrent disease with scars and sinus tract formation that causes substantial impact on quality of life. For evaluation of HS and treatment results, a scoring system for disease severity (Hidradenitis Suppurativa Score, HSS) has been proposed. Objectives To describe the interobserver reliability of the HSS and further to document its correlation with risk factors and other measures of disease severity. Methods Sixty-one consecutive patients with HS, referred to a clinical centre with special interest in the disease, were scored according to the HSS protocol: eight patients by four dermatologists together, 23 patients by all four observers independently and 30 patients by a single observer. Interobserver variability in HSS between the four observers was investigated in the group of 23 patients. Patients' reports of weight and height, smoking habits etc., were collected, as well as Dermatology Life Quality Index (DLQI) questionnaires. Results The interobserver concordance of HSS was 0·95. Median (interquartile range, IQR) HSS for all patients was 40 (18-73); women 39 (16-68); men 60·5 (30-95). Median (IQR) HSS for nonsmokers was 26 (12-65); former smokers 30 (10-56); smokers 44 (26-108). Median (IQR) HSS for normal weight patients was 12 (10-30); overweight 43 (25-58); obese 51 (24-95). Mean ± SD DLQI for all patients was 11·3 ± 8·6. Conclusions HSS is simple to use and shows low interobserver variability. The score correlates with suggested risk factors, indicating that it reflects a valid estimation of disease severity.