Nephrotic syndrome (NS), characterized by proteinuria >3.5 g daily and hypoalbuminemia (± oedema and dyslipidemia) is one of the leading manifestations of various glomerular diseases, both primary and secondary (systemic autoimmune diseases, diabetes mellitus, amyloidosis, monoclonal gammapathy, malignancy, infections, drugs, etc). Kidney biopsy is usually required to establish the cause of NS in adult patients and to choose optimal treatment. In a review article, the authors discuss the most common ethiological factors of NS and its differential diagnosis.