Diabetes mellitus (DM) is a worldwide health problem due to its high prevalence, incidence and impact on patient morbidity and mortality. Chronic kidney disease (CKD) is one of the most important complications of DM. The indication of renal biopsy in diabetic patients is a widely debated topic and the final decision is usually individualized. The results of renal biopsy in diabetic patients can be classified into three groups: diabetic nephropathy (DN), non-diabetic renal disease (NDRD) or DN plus NDRD (mixed forms). Renal involvement in DN has been widely studied and different pathological classifications have been proposed. Some groups demonstrated a relationship between the pathological classifications in DN and renal prognosis. However, to our knowledge renal biopsy in diabetic patients with DN has not demonstrated an impact on their survival and renal prognosis. Some recent studies suggest that non-proteinuric diabetic patients may be affected of DN. In addition, kidney biopsy in DN under new treatments may have a fundamental role in assessing renal protection or even regression of diabetic histological lesions. On the other hand, the accurate and early diagnosis and subsequent treatment of diabetic patients with NDRD has been shown to benefit both their renal and patient prognosis. Renal involvement in patients with DM is very heterogeneous. Thus, the role of renal biopsy in diabetic patients is becoming increasingly important.