Diagnosis of Alport syndrome or Thin basement membrane disease is suggested first of all by the clinical picture, the presence of neurisensorial hypoacusia and/or ocular abnormalities, and the family history which should be as accurate as possible involving the largest number possible of family members to recognize the transmission modalities, i.e. X-linked or autosomal. Renal biopsy remains the main tool to confirm the diagnosis and requires electron microscopy observation and collagen IV alpha chains investigation on renal tissue by means of specific antibodies. Skin biopsy is a useful and less invasive tool in families with X-linked Alport syndrome and can substitute renal biopsy in childhood as well as in patients with contraindication to renal biopsy. Confocal microscopy is mandatory to reduce the risk of false negative results in patients with segmental expression of alpha chains. Genetic analysis is at present indicated for studying subjects at risk for family planning or possible kidney donation but new techniques (Next Generation Sequencing) might increase their use in clinical practice.