The clinical guidelines for interstitial cystitis and related symptomatic conditions were revised by updating our previous guidelines. The current guidelines define interstitial cystitis/bladder pain syndrome as a condition with chronic pelvic pain, pressure or discomfort perceived to be related to the urinary bladder accompanied by other urinary symptoms, such as persistent urge to void or urinary frequency in the absence of confusable diseases. The characteristic symptom complex is collectively referred as hypersensitive bladder symptoms. Interstitial cystitis/bladder pain syndrome is divided into Hunner-type interstitial cystitis and bladder pain syndrome; Hunner-type interstitial cystitis and bladder pain syndrome represent interstitial cystitis/bladder pain syndrome with Hunner lesions and interstitial cystitis/bladder pain syndrome without Hunner lesions, respectively. So-called non-Hunner-type interstitial cystitis featured by glomerulations or bladder bleeding after distension is included in bladder pain syndrome. The symptoms are virtually indistinguishable between Hunner-type interstitial cystitis and bladder pain syndrome; however, Hunner-type interstitial cystitis and bladder pain syndrome should be considered as a separate entity of disorder. Histopathology totally differs between Hunner-type interstitial cystitis and bladder pain syndrome; Hunner-type interstitial cystitis is associated with severe inflammation of the urinary bladder accompanied by lymphoplasmacytic infiltration and urothelial denudation, whereas bladder pain syndrome shows little pathological changes in the bladder. Pathophysiology would also differ between Hunner-type interstitial cystitis and bladder pain syndrome, involving interaction of multiple factors, such as inflammation, autoimmunity, infection, exogenous substances, urothelial dysfunction, neural hyperactivity and extrabladder disorders. The patients should be treated differently based on the diagnosis of Hunner-type interstitial cystitis or bladder pain syndrome, which requires cystoscopy to determine the presence or absence Hunner lesions. Clinical studies are to be designed to analyze outcomes separately for Hunner-type interstitial cystitis and bladder pain syndrome.