Flat Carcinoma <i>in situ</i> of Bladder

36 patients with flat carcinoma in situ of the bladder have been reviewed. Those with widespread disease usually presented with dysuria or obstructive outflow tract symptoms and radical surgery appeared to give better results than radiotherapy. However, when the lesion was confined to small areas of the bladder mucosa, haematuria or pain were the main presenting symptoms and a conservative approach seemed justified. It is suggested that the term flat carcinoma in situ be used for this lesion whose behavior differs significantly from that of the commoner papillary or invasive tumours. The pathological appearances are to be reported elsewhere in full.