The internal consistency and construct validity of the RULS-8, a brief measure of loneliness for use with adolescents, was examined in three samples of Dutch-speaking adolescents in Belgium (for a total of N = 6,236). The measure showed high levels of internal consistency (ranging between .80 and .82), strong convergence with the original 20-item instrument (r = .92; Sample 1; N = 282), excellent fit with its hypothesized factor structure through confirmatory factor analysis (Sample 2; N = 1,144), measurement invariance across gender, and significant correlations in the expected direction with a set of indicators of psychological adaptation and maladaptation (Sample 3; N = 4,810). Based on these results, the 8-item short form is recommended for use with Dutch-speaking adolescents when administration of the full form seems less advisable due to time constraints. Suggestions for potential use of the short form and for future research on its reliability and validity are outlined. Keywords: loneliness, adolescence, UCLA short form, internal consistency, construct validity