Various aspects of the histological appearance of the bladder wall in interstitial cystitis have been emphasized over the 75 years since Hunner described the condition. The major focus of interest in this disease during the last decade has been the study of the relative significance of detrusor mastocytosis. Although this was for some years considered pivotal in establishing a diagnosis of interstitial cystitis, most recent studies have not shown mastocytosis to be a consistent feature of the disease. The histological picture of this condition is now considered to be that of a chronic inflammatory infiltrate of the lamina propria, possibly with fibrosis of the detrusor or lamina propria. The authors attempted to determine if there is a correlation between the severity of inflammation and fibrosis, and detrusor mastocytosis, on initial biopsy and the response of symptoms to conservative treatment. Of 39 patients, 10 required major surgical intervention. Although not reaching statistical significance, most cases with mild disease responded to conservative management. However, over 50% of cases showing severe histological disease also responded well to this type of treatment. Histological assessment of the interstitial cystitis bladder is more useful in ruling out other diseases than in allowing the demonstration of specifical diagnostic features of this condition. A severely abnormal microscopic picture does not necessarily indicate a poor prognosis.