Whether early vs. delayed referral to septal reduction therapies (SRT, alcohol septal ablation or surgical myectomy) bears prognostic relevance in hypertrophic obstructive cardiomyopathy (HOCM) is unresolved. We analyzed the impact of SRT timing on the outcome of HOCM patients.We followed 126 patients for 5 ± 4 years after SRT (mean age 53 ± 15 years; 55 post-ASA and 71 post-SM). Based on time-to-treatment (TTT; from HOCM diagnosis to SRT), patients were divided into three groups: "3" years, N = 50; "3-5" years, N = 25; "5" years, N = 51.Patients with TTT 5 years were younger at diagnosis and more often had atrial fibrillation (AF). Left ventricular outflow tract (LVOT) gradients were comparable in the 3 TTT groups. Two patients died peri-operatively, all with TTT 5. Long-term, 8 patients died (3 suddenly and 5 due to heart failure). Mortality increased progressively with TTT (2% vs. 4% vs. 12% for TTT "3", "3-5", and "5" years, p for trend = 0.039). Independent predictors of disease progression (new-onset AF, worsening to NYHA III/IV symptoms, re-intervention or death) were TTT ("3-5" vs. "3" years: HR: 4.988, 95%CI: 1.394-17.843; "5" vs. "3" years: HR: 3.420, 95%CI: 1.258-9.293, overall p-value = 0.025), AF at baseline (HR: 1.896, 95%CI: 1.002-3.589, p = 0.036) and LVOT gradient (HR per mm Hg increase: 1.022, 95%CI: 1.007-1.024, p = 0.023).Delay in SRT referral has significant impact on long-term outcome of patients with HOCM, particularly when5 years from first detection of gradient, even when successful relief of symptoms and gradient is achieved. Earlier interventions are associated with lower complication rates and better prognosis, suggesting the importance of timely SRT to maximize treatment benefit and prevent late HOCM-related complications.