Background: Obesity is a major public health challenge and one of the leading drivers of multimorbidity worldwide. This study aimed to assess the burden of sickness absence attributed to obesity (International Classification of Diseases, 10th Revision – ICD-10, code E66) in Poland by analyzing temporal trends, demographic patterns, geographic variation, and associated social insurance expenditures 2020–2025. Material and Methods: This nationwide registry-based study used administrative data from the Social Insurance Institution (Zakład Ubezpieczeń Społecznych). All sickness absence certificates attributed to obesity (2020–2025) were analyzed. Indicators included sickness absence days, sickness absence certificates, average sickness absence duration, and social insurance expenditures. Analyses were stratified by sex, age group, year, and geographic area. Results: Sickness absence days attributed to obesity increased from 134 977 in 2020 to 338 391 in 2025 (+150.7%), while sickness absence certificates increased from 7395 to 21807 (+194.9%). Corresponding rates increased from 352.7 to 902.6 days and from 19.3 to 58.2 certificates per 100 000 population. The estimated annual percentage change (APC) was 20.9% (95% CI: 12.0–30.6) for sickness absence days and 25.1% (95% CI: 15.5–35.5) for certificates. The increase was more pronounced among females than males, with APCs of 22.7% vs. 16.6% for sickness absence days and 26.7% vs. 21.1% for certificates, respectively. The highest burden was observed among individuals aged 35–49 years, with considerable regional variation. Average sickness absence duration decreased from 5.83 to 4.12 days per certificate. Social insurance expenditures increased from PLN 9.5 million in 2020 to PLN 31.8 million in 2024 (+235.4%). Conclusions: Sickness absence attributed to obesity (ICD-10 code E66) increased substantially in Poland in 2020–2025, particularly among women and middle-aged adults. These findings highlight the growing relevance of obesity for occupational health and support workplace-based prevention and early identification of workers at increased risk of work incapacity. Med Pr Work Health Saf. 2026;77(6)