OBJECTIVESTo investigate the expression of CD44 protein in bilharzial and non‐bilharzial bladder carcinomas, and to relate the results of immunohistochemistry to the established prognostic factors, as studies clearly show that altered adhesive function of tumour cells is important in the metastatic process and CD44 is assumed to be critical in the malignant progression of many human tumours.PATIENTS AND METHODSThe study included 55 patients with bladder carcinoma confirmed by cystoscopy and biopsy. Of the 33 patients with transitional cell carcinoma (TCC), 19 were bilharzial and 14 non‐bilharzial, and of 22 with squamous cell carcinoma (SCC), 12 were bilharzial and 10 non‐bilharzial. CD44 expression was measured by immunohistochemical analysis of paraffin‐embedded tissue obtained from these patients after appropriate treatment (transurethral resection, partial or radical cystectomy).RESULTSThere was significantly less CD44 expression in invasive TCC than in normal urothelium and pre‐invasive TCC (P = 0.05). The expression of CD44 was inversely related to the tumour grade and depth of invasion (P = 0.05). However, there was no such relation for SCC; there was no significant difference between CD44 expression in metaplastic squamous epithelium, pre‐invasive and invasive SCC. The presence or absence of bilharzial ova had no apparent effect on the expression of CD44, with no significant difference between CD44 expression in bilharzial and non‐bilharzial bladder carcinomas.CONCLUSIONSThese data confirm that there is a reduction in CD44 expression with increasing tumour grade and stage of TCC, and may provide an additional aid in predicting the progression of this tumour. There was no such relationship with SCC, and no difference between CD44 expression in bilharzial and non‐bilharzial bladder carcinomas.