This study aims to adapt and validate the Bulgarian version of the Social and Emotional Loneliness Scale on adults and older adults. We present the results of the psychometric assessment of the questionnaire on a sample of adults aged 35-75 (N=332; Mage=49.45; SD=11.17). Exploratory factor analysis revealed four factors: Two factors were identical to the first two sub-scales, the third sub-scale split into two separate factors. Reliability of the new sub-scales was assessed with Cronbach's α coefficient that showed high levels of reliability for the general scale (α=0.875) and for all four sub-scales (α ranged from 0.843 to 0.873). Confirmatory factor analysis proved the four-factor structure of the adapted scale. The convergent validity of the Social and Emotional Loneliness Scale was proved by correlation analysis with the Differential Questionnaire of Loneliness Experience. Our study yielded the adequate psychometric characteristics of the Social and Emotional Loneliness Scale for adults and older adults in Russia. In future research, we plan to increase the sample to standardize the scores for the scales.