Purpose: Diabetes mellitus (DM) is a relevant risk factor for enhanced susceptibility to and adverse outcomes in infections, including community-acquired pneumonia (CAP). We aimed to characterise clinical outcomes, inflammatory and organ failure markers and microbial etiologies in diabetic (DM+) versus non-diabetic (DM−) patients in a European CAP cohort. Methods: Comparative analyses using data from the CAPNETZ multicenter, prospective, observational study including 13,611 patients with CAP enrolled between 2002–2022, with and without a history of DM, were conducted. Results: Seventeen percent (2310/13,611) had a history of DM (DM+). Compared to DM− patients, DM+ patients had a higher 180 days mortality rate following CAP (13% (292/2310) vs. 7% (766/11,301), p < 0.0001) and higher C-reactive protein and leucocyte counts (median CRP 97 mg/L (IQR: 31–202) vs. 86 mg/L (IQR: 24–190), p < 0.0001; median leucocyte count 12/nl (IQR: 9–16)vs. 11/nl (IQR: 8–15), p < 0.0001). Pathogens were identified in 23.4% (540/2310) of the DM+ and 21.7% (2414/11,301) of the DM− patients (p = 0.03), respectively. Overall, pathogen distribution differed between the two groups, with higher frequencies of Enterobacteriaceae in the DM+ group (13.0% (70/539) vs. 8.0% (194/2414), p_adj < 0.01). Conclusions: CAP in DM+ is characterised by a distinct microbial spectrum and enhanced inflammation. While further studies are needed to elucidate the clinical impact of our findings, we recommend early and comprehensive CAP pathogen testing in DM+ patients.