Background: The etiology of hidradenitis suppurativa (HS) involves genetic and environmental factors. Well-established associated systemic factors are obesity, smoking, inflammation, and bacteria. Whether localized environmental factors such as friction and pressure may also play a causative role is still unclear. Objective: To describe the possible Koebner phenomenon (KP) in HS. Methods: The case notes on 14 patients with typical HS and additional HS lesions in previously uninvolved skin areas exposed to mechanical stress, e.g., on the abdomen at the level of the waistband, were reviewed with regard to the clinical characteristics of the cohort. Results: All 14 patients (7 females) were obese with a mean BMI of 35.8 (range 30.1-45.0). All patients developed additional ectopic HS lesions at the sites of friction on the convex abdomen. The ectopic lesions were clinically and histopathologically similar to HS. Conclusion: Mechanical stress factors or trauma play a role in obese patients with HS. It is suggested that these new induced lesions fit the concept of the KP. This phenomenon seems to occur in the so-called frictional furunculoid type of HS and may explain the unique distribution at certain localizations on the body of this follicular cutaneous eruption. Removal in an early stage of HS of external stress factors that can lead to the KP should be part of the treatment, especially in obese patients.