Evaluation of mitral (MA) and tricuspid annuli (TA) in the same healthy subject in a non-invasive way in real-life clinical settings makes an opportunity to compare their dimensions and derived functional properties. The purpose of the present cohort study was to investigate whether there are any differences in the three-dimensional speckle-tracking echocardiography- (3DSTE-) measured size and derived functional characteristics of the MA and TA in the same healthy adults. The study comprised 248 healthy adults, in which 3DSTE was performed to determine MA and TA dimensions and functional properties. Due to insufficient image quality, 89 cases were excluded, therefore the remaining population consisted of 159 subjects (age: 35.6±12.9 years, 76 males). Subjects were enrolled on a voluntary basis consecutively between January 2011 and November 2017 in the outpatient clinic of the tertiary cardiology center at the Department of Medicine, University of Szeged, Hungary. Data were analyzed by Student's t-test, analysis of variance (ANOVA) test, Fischer's exact test, Pearsons' correlations, interclass correlations and Bland-Altman tests. Same-side MA/TA end-diastolic annular dilation is associated with simultaneous MA/TA end-systolic dilation and vice versa. MA dilation in end-diastole and end-systole results in MA functional improvement/deterioration. Dilation of end-diastolic TA dimensions does not obviously entail differences in TA function. However, similar to MA, more dilated TA in end-systole is associated with impaired TA function. Dilated MA dimensions (end-diastolic MA area: 4.31±0.62 vs. 10.89±1.18 cm2, P<0.05) are not obviously associated with dilated end-diastolic TA dimensions (area: 7.05±1.42 vs. 7.81±1.48 cm2, P=ns) and functional improvement/impairment (fractional area change: 27.5%±10.8% vs. 25.2%±10.6%, P=ns). Dilation of MA and TA is associated with different contralateral responses in morphology and function.