Background <p>Loneliness is a prevalent and complex phenomenon influenced by various social and demographic factors. The goal of this study was to translate the Three-Item UCLA Loneliness Scale into Croatian and test its validity and reliability in practice. An additional aim was to explore the relationship between social connectedness and loneliness within the Croatian population, with respect to age and gender.</p> Method <p>The Three-Item Loneliness Scale was translated into Croatian and validated according to widely accepted guidelines for cross-cultural adaptation and translation of the questionnaire into different languages. Subsequently, loneliness and social connectedness were examined in 309 Croatian participants using an anonymous online survey.</p> Results <p>The results indicated a&#xa0;significant association between social connectedness and loneliness. In particular, those with fewer individuals in their social network were associated with higher loneliness. Notably, age had a significant negative association with loneliness, indicating increased loneliness among younger individuals. Meanwhile older individuals with fewer active network domains experienced heightened loneliness compared to other age groups. No effect of gender was observed.</p> Conclusion <p>Our findings highlight the importance of social connectedness in relation to loneliness, particularly among younger and older age individuals. This study, through its validation of the instrument for measuring loneliness, offers important insights into the unique Croatian context, emphasizing how cultural and social factors may influence the experience of loneliness and social connectedness.</p>