Renal tubular acidosis (RTA) is a tubulopathy characterized by metabolic acidosis with normal anion gap secondary to abnormalities of renal acidification. RTA can be classified into four main subtypes: distal RTA, proximal RTA, combined proximal and distal RTA, and hyperkalemic RTA. Distal RTA (type 1) is caused by the defect of H(+) secretion in the distal tubules and is characterized by the inability to acidify the urine below pH 5.5 during systemic acidemia. Proximal RTA (type 2) is caused by an impairment of bicarbonate reabsorption in the proximal tubules and characterized by a decreased renal bicarbonate threshold. Combined proximal and distal RTA (type 3) secondary to a reduction in tubular reclamation of bicarbonate and an inability to acidify the urine in the face of severe acidemia. Hyperkalemic RTA (type 4) may occur as a result of aldosterone deficiency or tubular insensitivity to aldosterone. Clinicians should be alert to the presence of RTA in patients with an unexplained normal anion gap acidosis, hypokalemia, recurrent nephrolithiasis and nephrocalcinosis. The mainstay of treatment of RTA remains alkali replacement.