Bicuspid aortic valve (BAV) disease has a male predominance of approximately 3:1 and shows diverse presentations about aortic valve dysfunction. This study aimed to find independent determinants for significant aortic stenosis (AS) or significant aortic regurgitation (AR) in adults with BAV. We retrospectively investigated the medical records of 1,073 subjects (773 men, mean age 55 ± 14 years) who were first diagnosed with BAV disease by transthoracic echocardiography. We excluded 52 subjects with both significant AS and significant AR. Of the remaining 1,021 subjects, 418 (41%) presented with significant AS, 249 (24%) showed significant AR, and the rest of the subjects were grouped into a normal functioning BAV (n = 354, 35%). BAV morphology was classified into the following 4 types according to position and pattern of raphe and cusps: (1) fusion of the right and left coronary cusps (type 1), (2) fusion of the right and noncoronary cusps (type 2), (3) fusion of the left and noncoronary (type 3), and (4) no raphe (type 0). Patients with significant AS were older, more likely to be women than men, and had a higher prevalence of type 0 BAV. Patients with significant AR were younger and were more likely to be men. In multivariate logistic regression analysis, women, older age, and type 0 or type 3 BAV were associated with significant AS. In contrast, men, hypertension, and chronic kidney disease were correlated with significant AR. Significant valve dysfunction in adults with first diagnosed BAV was closely associated with age, gender, and BAV morphology.