['CD151 belongs to the group of tetraspanins and is aberrantly expressed in different tumours and differential expression has been associated with prognosis. The aim of this study was to clarify the relationship of CD151 expression with tumour phenotype and clinical outcome in bladder cancer.', 'A bladder cancer tissue microarray containing samples from 686 urothelial bladder cancers was analysed by immunohistochemistry.', 'Membranous CD151 immunostaining was recorded in 409 (66.0%) of 620 analysable cases. High CD151 expression was seen in normal urothelium and in most non-invasive tumours. Low CD151 expression levels were associated with a more unfavourable tumour phenotype. CD151 staining was seen in 71.5% of 284 pTa, 62.1% of 145 pT1 and 60.4% of 187 pT2-4 cancers (p\u200a=\u200a0.0033). CD151 staining was detectable in 77.3% of 75 grade 1, 71.1% of 273 grade 2 and 57.7% of 272 grade 3 cancers (p\u200a<\u200a0.0001). CD151 expression status was not associated with overall or tumour-specific survival in muscle-invasive cancers (pT2-4), tumour progression in pT1 and recurrences in pTa tumours.'] Is reduced CD151 expression related to advanced tumour stage in urothelial bladder cancer?