The cardiothoracic ratio (CTR) is a clinical criteria used to estimate heart size and possible linked abnormality, such as cardiomegaly, from chest X-ray (CXR) images. Visual evaluation of CTR in clinical practice is time-consuming and may introduce variation across interpreters. Obtaining the objective measurement of CTR in an automatic way will decrease the subjectivity of the radiologist’s evaluation and will give more support to their diagnosis during follow-up examinations. The goal of this thesis was to investigate the automatic measurement of the CTR. Two segmentation-based approaches have been proposed for the calculation of the CTR from CXR images. A first method estimates the CTR based only on lung segmentation, and a second method adds the segmentation of the heart for the estimation of the CTR.