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Background: There is limited data on the progression of the scar on LGE in patients with hypertrophic cardiomyopathy (HCM) stratified by age and its relationship with sudden cardiac death (SCD). Objectives: We compared LGE progression as stratified by age and examined the relationship of this risk to SCD. Methods: A total of 102 HCM patients (age <60 years; n=75, age ≥60 years; n=27) undergoing two consecutive cardiovascular magnetic resonance (CMR) at an interval of 4.3 ± 3.3 years from two medical centers were evaluated. LGE was quantified semi-automatically using a 6-SD threshold followed by manual adjustment. Median follow-up from study entry to the most recent evaluation was 7.3 years. The primary endpoint was the composite of resuscitated cardiac arrest and SCD. Results: At the first CMR, LGE was detected in 61 (60%) patients. At the follow-up, 25 patients developed a new LGE; thus, 86 (84%) patients had LGE by the follow-up CMR. Overall, the progression rate was 0.7 ± 1.0%/year, including 21 patients (21%) with LGE progression ≥1% /year and 5 (5%) with LGE >15% at follow-up. The risk of LGE progression ≥1%/year was significantly higher in patients <60 years (25% vs. 7%, p=0.02). There was a trend for the highest risk of LGE progression ≥1%/year in patients <60 years with LGE >10% at baseline scan. LGE progression ≥1%/year was a strong predictor of the primary outcomes (HR 1.88 [95% CI; 1.08-3.26], p=0.03). LGE progression moderately correlated with changes in LV mass, indexed LV mass index, and maximal LV end-diastolic wall thickness (p<0.001 for all). Conclusions: Progressive fibrosis occurs more frequently in young to middle-aged HCM patients and identifies a cohort at high risk of SCD. One-quarter of young to middle-aged patients exhibit LGE progression ≥1%/year, underscoring the importance of repeating CMR to re-evaluate for potential LGE progression in this age group.