Background: Chronic kidney disease (CKD) affects up to 40% of individuals with diabetes mellitus. Given the fact that CKD in diabetics may result from various non-diabetic renal disorders, kidney biopsy remains essential in cases with atypical clinical presentation. The aim of this study was to assess the prevalence of diabetic nephropathy (DN) and other non-diabetic kidney diseases (NDKD) among diabetic patients who underwent renal biopsy. We also tried to find clinical and laboratory markers predicting the presence of DN in renal tissue. Methods: A retrospective analysis of all native renal biopsies in diabetic patients performed between 2010 and 2024 in one European nephrology center. Results: The cohort included 115 diabetic patients. DN was diagnosed in 43.5% individuals. Among NDKD cases, vasculitis (8.7%), membranous nephropathy (7.8%), and amyloidosis (7.8%) were most frequent. Compared with the NDKD group, patients with DN were younger, had a longer duration of DM, more often required insulin therapy, more frequently demonstrated diabetic retinopathy (DR) and nephrotic syndrome, and exhibited higher HbA1c levels. In multivariable logistic regression, younger age, need for insulin therapy, and presence of DR were the strongest predictors of DN. Conclusions: NDKD is common among DM patients. Patient’s younger age, the need for insulin therapy, and the presence of DR are strong predictive markers for diabetic nephropathy. Renal biopsy remains the most accurate method for diagnosis and should be considered in every case of suspected NDKD.