Cytologic and histopathologic study of 36 patients demonstrated an 86 to 92 per cent incidence of squamous metaplasia of the bladder among patients with chronically infected bladders and a 64 per cent incidence in patients with postdiversionary bladders left behind. The relationships of infection, inflammation, squamous meetaplasia, and squamous cell carcinoma of the bladder are reviewed. It is postulated that the same carcinogenic factors which induce transitional cell carcinoma might cause squamous cell carcinoma if the epithelium had previously undergone squamous metaplasia.