I am participating in a study on Cross-cultural validation of an expanded Exercise Addiction Inventory. The first part of the research was dedicated to data collection. The EAI-3 was administered to over 5000 regular exercisers in 15 languages through an online survey. My responsibility and focus were put on two countries, Serbia and Croatia. The survey also included questions from the Exercise Dependence Scale-Revised, the Obsessive-Compulsive Inventory-Revised, the SCOFF questionnaire, and the Ten Item Personality Inventory. The second part is dedicated to investigating the factorial structure of the EAI-3 for countries mentioned as the primary goal of my thesis. Exercise addiction (EA) is characterized by excessive exercise, lack of control, and potential health risks. The Exercise Addiction Inventory (EAI) is one of the most widely used tools in its assessment. However, the cross-cultural psychometric properties of the EAI could be improved; therefore, the present study aimed to validate an expanded eight- items version of the EAI (EAI-3) in a large international sample. The assessment structure and the reliability of the EAI-3 were tested with factorial analysis and thought measurement invariance across languages and sex while identifying standard cutoff points for at-risk exercisers. My thesis reflects both the positive and pathological sides of exercise. It indicates that the structure has excellent reliability and goodness-of-fit. The configural and metric invariance of the scale was also supported. The conclusion suggests that the EAI-3 is a promising tool for screening EA in an international sample, with a robust and reliable structure comparable across languages and sex. The proposed cutoff could pave the way toward a consensus on a threshold to screen for EA.