The key to successful therapy of interstitial cystitis (IC) is to correctly diagnose it. The significant majority of patients with IC have a dysfunctional bladder epithelium that allows urinary solutes (primarily potassium) to leak into the bladder wall, causing symptoms and tissue damage. Drugs that correct this dysfunction and suppress symptoms are important to achieve successful outcomes in patients. Today over 95% of females with IC are misdiagnosed as having gynecologic chronic pelvic pain, vulvodynia, vaginitis, endometriosis, overactive bladder or urinary tract infection. Men are misdiagnosed as having prostatitis. Often children are not diagnosed at all. Multimodal drug therapy may be required and can achieve successful resolution of IC in over 90% of patients. IC in children can be treated successfully with pentosan polysulfate.