The anti-tumour necrosis factor (TNF)- adalimumab is the only licenced biologic for moderate-to-severe hidradenitis suppurativa (HS). No predictors of response have been identified so far.To identify clinical parameters predicting response to adalimumab and confirm its efficacy/ safety.Data of 389 HS patients treated with adalimumab in 21 Italian centres were reviewed. Sex, ages at onset/diagnosis/baseline, body mass index, smoking, phenotypes, previous treatments, concomitant antibiotics , and "therapeutic delay", defined as the time from HS onset to adalimumab initiation, were assessed. Response to adalimumab and its impact on quality of life (QoL) were evaluated using "Hidradenitis Suppurativa Clinical Response" (HiSCR) and "Dermatology Life Quality Index" (DLQI)/"Visual Analogue Scale for pain" (VAS pain), respectively. Logistic regression analysis was performed.The "therapeutic delay" correlated to lack of response to adalimumab at week 16 (OR,1.92 for therapeutic delay 10 years; 95% CI,1.28-2.89; P=0.0016). HiSCR was achieved in 43.7% and 53.9% patients at week 16 and 52, respectively. Significant reductions in both DLQI and VAS pain were found between week 16 versus baseline (p<0.0001 for both) and week 52 versus baseline (p<0.0001 for both). Previous immunosuppressants inversely correlated to HiSCR at week 52 [OR=1.74, 95% CI 1.04-2.91, p=0.0342].Inverse correlation between therapeutic delay and clinical response was found, supporting early adalimumab use and providing evidence for a "window of opportunity" in HS. Adalimumab efficacy and safety were confirmed, along with patients' QoL improvement. Immunosuppressants could negatively influence response to adalimumab inducing a switch to non-TNF -driven pathways.