Background This study investigated the influence of African/Afro-Caribbean (black) ethnicity on the clinical profile and outcomes in hypertrophic cardiomyopathy (HCM). Methods 425 consecutive patients with HCM (163 black and 262 Caucasians (white); mean age 52.5±16.6â .years) were assessed at three cardiomyopathy centres. Repeat assessments were performed every 6-12 months and mean follow-up was 4.3±3.0years. The primary outcome was a composite of cardiovascular death, cardiac arrest or appropriate device therapy. Results A fortuitous diagnosis of HCM was more commonly made in black compared with white patients (31.3% vs 19.1%, p=0.004). An abnormal ECG at presentation was more frequent in black patients (98.2% vs 90.5%, p=0.002), with T-wave inversion being a common feature (91.4% vs 73.0%, p<0.001). Asymmetric septal hypertrophy was the predominant pattern in both ethnic groups; however, apical (22.2% vs 10.7%, p<0.001) and concentric (9.3% vs 1.5%, p<0.001) patterns were more prevalent in black patients. Hypertension was more frequent in black patients (58.3% vs 31.7%, p<0.001). There were no ethnic differences in risk factor profile or primary outcome. Independent predictors of the primary outcome were non-sustained ventricular tachycardia (HR 6.03, 95% CI 3.06 to 11.91, p≤0.001) and hypertension at presentation (HR 2.02, 95% CI 1.05 to 3.88, p=0.036), with an additive effect. Conclusion Black ethnicity is an important determinant of the phenotypic expression of HCM but does not adversely affect outcomes. Apical and concentric hypertrophy are common in black patients and may hinder the identification of HCM in this cohort. Hypertension has an adverse effect on outcome, irrespective of ethnicity.