Background: The reported mean age of onset of hidradenitis suppurativa (HS) is between 20 and 24 years. Prepubertal onset is thought to be rare. Objective: We sought to determine the prevalence of early-onset HS and to compare clinical characteristics between early-onset and normal-onset HS in a retrospective study. Methods: Data were collected from 855 patients with HS. Early-onset HS was defined as onset before the thirteenth birthday. Clinical characteristics were analyzed in relation to the age of onset. Results: In all, 66 patients (7.7%) reported early-onset HS. A family history for HS was significantly higher in early-onset patients (55.6% vs 34.2%; odds ratio 2.1, 95% confidence interval 1.2-3.6, P = .006). They developed inflammatory lesions at more body sites than patients with normal-onset HS (odds ratio 3.0, 95% confidence interval 1.8-4.9, P < .001). Distribution of the Hurley stages of severity showed no differences between the 2 groups (odds ratio 1.1, 95% confidence interval 0.7-1.8, P = .72). Limitations: Some data were based on patient-reported information. Conclusion: Early-onset HS occurs more frequently than previously believed. Patients with early-onset HS often report a family history for HS and develop lesions at more body sites.