Objectives: The aim of this study is to examine social functioning as a key domain of obesity-related quality of life (QoL) using the updated Obesity Quality of Life Instrument (OQI-3) v. 2. Material and Methods: The study was conducted in 2024 among adult patients diagnosed with obesity treated at a hospital dietary clinic in Warsaw, Poland. The study continued the validation work on the OQI-3 instrument following a pilot study. The updated OQI-3 v. 2 consists of 3 sections: 1) gender-adjusted workplace vignettes assessing perceived attitudes and emotions, 2) a multiple-choice list of obesity-affected daily activities, and 3) a 16-item Likert scale assessment of the impact of obesity on daily functioning. Descriptive analyses, item analysis, internal consistency reliability, and principal component analysis (PCA) were performed. Results: A total of 164 participants were included (125 women and 39 men), with BMI of mean ± standard deviation 40.91±7.68 kg/m², corresponding to class III obesity. The vignette-based section revealed predominantly negative workplace experiences, including discomfort, unfriendly behaviors, and reduced interest, accompanied mainly by emotions such as sadness, stress, frustration, and reduced self-worth. In the daily activities section, rapid fatigability was the most frequently reported difficulty, followed by problems with climbing stairs, poor physical condition, and clothing size issues. The third section demonstrated high internal consistency (Cronbach’s α = 0.895). Principal component analysis identified 3 components – interpersonal functioning, self-care, and physical activity – explaining 58.55% of the total variance, each showing satisfactory to very good reliability (α = 0.714–0.877). Conclusions: Obesity Quality of Life Instrument v. 2 may be a reliable and psychometrically solid tool for assessing obesity-related quality of life, with particular strength in capturing impairments in social and interpersonal functioning. The findings highlight the substantial impact of obesity on workplace experiences, daily activities, and social relationships, supporting the relevance of social functioning as a critical QoL domain in adults with obesity. Int J Occup Med Environ Health. 2026;39(3)