Recognition of early invasion (stage pT1) in urothelial neoplasia is one of the most challenging areas in bladder pathology, and reproducibility between pathologists is a major issue. This fact, together with the proposal by some urologists to treat early invasive tumours more aggressively, makes the accurate detection of pT1 lesions even more relevant in clinical practice. In recent years, the morphologic features and patterns of invasion of tumour into the lamina propria have been more accurately characterised and standardised, and although some of the features are subtle, they can be of great utility in the accurate assessment of pT1 staging. Histologic grade, changes at the stroma-epithelial interface, the characteristics of the invading epithelium, and the stroma-associated response are among the most important clues for appropriate pT1 staging and these are discussed in this review. Common problems in stage pT1 disease evaluation include, tangential sectioning--due to an inability to orient transurethral resection specimens--crush and cautery artefacts, and a streaking inflammatory infiltrate. With few exceptions, the criteria discussed in this review allow pathologists to separate superficial bladder tumours consistently and reproducibly into non-invasive (pTa) tumours and tumours that have invaded the lamina propria (pT1), the latter having a significantly poorer prognosis. This review is intended to assist the surgical pathologist by presenting appropriate diagnostic criteria, by describing common pitfalls and by outlining the different histologic patterns of invasion of urothelial carcinoma into the lamina propria. The value of pT1 tumour substaging, as a predictor of bladder cancer progression is also discussed.