Background The increasing prevalence of multimorbidity among older people in Lithuania and other Central-Eastern European countries leads to a greater patient treatment burden and puts additional pressure on healthcare services. Objectives This study aimed to validate the Lithuanian version of the Multimorbidity Treatment Burden Questionnaire (MTBQ). Methods The Lithuanian version of the MTBQ was tested (2021-2022) with 789 patients from seven Lithuanian primary care centres who had two or more long-term conditions. The questionnaire translation’s reliability, validity and dimensionality of the were assessed with Spearman’s rank correlation, Cronbach’s alpha, and factor reduction analysis. Treatment burden and its associations with sociodemographic and other indicators were analysed. Results Lithuanian version of MTBQ had good internal reliability (Cronbach’s alpha 0.711), validity, factor reduction applicability, and interpretability. The MTBQ scores of the questionnaire had a negative association with the quality-of-life scale (r=-0.327, 95% CI [-0.389, −0.264]) and positive associations with the self-rated health scores (r = 0.230, 95% CI [0.163, 0.297]) and with the number of comorbidities (r = 0.164, 95% CI [0.097, 0.233]). Distribution of treatment burden was identified (none (19,4%), low (46,6%), medium (25%), high (9%)). High treatment burden was found to be associated with having five or more long-term diseases, taking five or more medications, having anxiety or depression and living in a rural area. Conclusion The study’s findings show that the MTBQ is applicable in assessing the treatment burden of multimorbid patients in Lithuania. Furthermore, the study demonstrates that Lithuanian patients with multimorbidity have average treatment burden scores similar to or higher than participants in previous MTBQ validation studies.