: Mitral valve pathology and mitral regurgitation (MR) are very common in patients with hypertrophic cardiomyopathy (HCM), and the evaluation of mitral valve anatomy and degree of MR is important in patients with HCM. The aim of our study was to examine the potential influence of moderate or moderately severe MR on the prognosis, clinical presentation, and structural characteristics of HCM patients. : A prospective study examined 176 patients diagnosed with primary asymmetric HCM. According to the severity of the MR, the patients were divided into two groups: Group 1 ( = 116) with no/trace or mild MR and Group 2 ( = 60) with moderate or moderately severe MR. All patients had clinical and echocardiographic examinations, as well as a 24 h Holter ECG. : Group 2 had significantly more often the presence of the obstructive type of HCM ( < 0.001), syncope ( = 0.030), NYHA II class ( < 0.001), and atrial fibrillation ( = 0.023). Also, Group 2 had an enlarged left atrial dimension ( < 0.001), left atrial volume index ( < 0.001), and indirectly measured systolic pressure in the right ventricle ( < 0.001). Patients with a higher grade of MR had a significantly higher E/e' ( < 0.001) and, as a result, higher values of Nt pro BNP values ( < 0.001) compared to Group 1. Kaplan-Meier analysis demonstrated that the event-free survival rate during a median follow-up of 88 (IQR 40-112) months was significantly higher in Group 1 compared to Group 2 (84% vs. 45% at 8 years; log-rank 20.4, < 0.001). After adjustment for relevant confounders, the presence of moderate or moderately severe MR remained as an independent predictor of adverse outcomes (HR 2.788; 95% CI 1.221-6.364, = 0.015). : The presence of moderate or moderately severe MR was associated with unfavorable long-term outcomes in HCM patients.