Left ventricular systolic and diastolic function can be assessed by studying mitral ring motion. Reference values for a wide range of age and body size are lacking however. The motion of the mitral ring was studied with M-mode echocardiography using the apical four- and two-chamber views. Data are reported as the average of measurements of four points on the mitral ring. Data were analysed using the stepwise multiple regression technique, with age, gender, height, weight, body surface area and heart rate as independent variables. A total of 70 healthy subjects were studied. In children and adolescents under age 18, there was strong correlation between mitral ring motion and body size, age and heart rate. The ring motion was best described as mitral ring motion (mm) = 2.2 + 0.078 x height (cm) (SEE = 1.0 mm). In adults, mitral ring motion was correlated with age, height and heart rate but not with weight or body surface area. Ring motion could be described from the following equations: mitral ring motion (mm) = 12.7 - 0.060 x age (years) + 0.031 x height (cm) (SEE = 1.2) or, if only age is taken into account, mitral ring motion = 18.4 - 0.065 x age (SEE = 1.2). In both children and adolescents up to age 18 and in adults, atrial contribution correlated significantly and positively to age and inversely to heart rate but not to height, weight, body surface area or gender. Atrial contribution was best described by the equation: atrial contribution = 0.15 + 0.0039 x age (SEE = 0.027). Thus, age and body size influences mitral ring motion and should be taken into account when interpreting patient data.