Abstract Background Individuals with diabetes mellitus (DM) exhibit several of comorbidity burdens, with lower perceived quality of life also being a factor. Literature on the impact of DM is available, including studies on the index devised by (A. Andreella et al., 2023) for the assessment of comorbidities of health conditions. This study aims to adapt and validate this index for use as a standardized DM comorbidity index within the EU. Methods A cross-sectional study was carried out using microdata from the European Health Interview Survey (EHIS) 2019. The study included adults aged 25 years or older who reported having DM (n = 20,042) from 27 EU member states. Comorbidity index was calculated to assess the comorbidity of having 9 non-communicable diseases using disability weights obtained from the Global Burden of Disease 2019 and self-perceived general health using multiplicative approach. Beta regression analysis was used to evaluate the association between comorbidity index and several demographic, socioeconomic and lifestyle variables. Comorbidity index was calculated for each nomenclature of territorial units for statistics (NUTS 2). Results The comorbidity index ranged from 0.049 to 0.993. The results indicated that having a higher education and residing in urban areas were less likely to have a high comorbidity index. Being unemployed or in other employment statuses demonstrated a significant, positive association with the index. Income exhibited a gradual, positive association with each quintile, while consuming fruits and vegetables less than once a week was found to be associated with an increased index. The highest comorbidity index was observed in Calabria (Italy), followed by Lubuskie (Poland), and the lowest was observed in Antwerp (Belgium), followed by Övre Norrland (Sweden). Conclusions By identifying comorbidity burden, targeted interventions and regional-specific strategies can be implemented to improve the quality of life for individuals with DM. Key messages • Quantifying the burden of comorbidities allows understanding of health status of DM patients. • Comorbidity index shows geographic variation in the EU which contributes to tailored policy interventions.