OBJECTIVES: Bicuspid aortic valve (BAV)-related aortopathy is increasingly recognized to be a heterogeneous disease entity, although the surgical approach, from indications to techniques, is still standard rather than individualized. We aimed to define the determinants of aortic dilatation in BAV patients stratified according to the valve morphotype. METHODS: A consecutive echocardiographic series of 622 BAV patients was analysed. Among demographic (age, sex), anthropometric (height, weight, body surface area, body mass index), clinical (associated diseases) and echocardiographic variables (valve function, ventricular parameters), the determinants of aortic root and ascending tract diameter were assessed by multivariate regression models, as well as the predictors of aortic dilatation (size index >2.1 cm/m(2)) both in the overall population and separately in groups of different valve morphotypes (RL, right-left fusion; RN, right-non-coronary fusion). RESULTS: Independent determinants of aortic root diameter (at sinuses) were age (P < 0.001), significant aortic regurgitation (P < 0.001), sex (female protective, P < 0.001) and valve morphotype (RN protective, P < 0.001). Independent determinants of ascending aortic diameter (tubular tract) were age (P < 0.001), RN morphotype (P < 0.001), body mass index (P = 0.005) and chronic obstructive pulmonary disease (P < 0.001). In univariate analysis, the RL morphotype was associated with dilatation (ASI > 2.1 cm/m(2)) at sinuses in 41% cases vs 22% for RN (P < 0.001), and the RN morphotype was associated with dilatation at the tubular tract in 68 vs 56% for RL (P = 0.007). The presence of root dilatation was predicted by age and absence of significant stenosis in the RL morphotype subgroup, and by severe regurgitation in the RN subgroup. In the RL-type subgroup, non-regurgitant aortic valve and chronic lung disease predicted dilatation at the ascending level; and in the RN-type subgroup, age and obesity. CONCLUSIONS: The two most common BAV morphotypes are associated with aortic dilatation at two different tracts (RL at the root; RN at the tubular ascending tract) independently of valve function. Moreover, the determinants of aortic dilatation were at least in part different between the two morphotypes: this may provide stratification criteria for individualized methods of follow-up and treatment.