Bladder tumours classically affect the elderly, but can also occur in young adults. The authors studied the prognosis of these tumours in patients under the age of 40. In their experience, these tumours represent 3.27% of all bladder tumours. 26 patients with a mean age of 34 years (20-40 years), 8 under the age of 30, were studied. There was a marked male predominance (23 males, 3 females). The tumour was a transitional cell carcinoma in 25 cases and a squamous cell carcinoma in 1 case. It was superficial in 11 cases and invasive in 15 cases. Transurethral resection and cystectomy were performed in 9 cases of superficial tumours and 11 cases of invasive tumours, respectively. In the group of superficial tumours, a favourable course was observed in 7 cases, with 3 cases of recurrence and 1 case of progression. In the group of invasive tumours, a favourable course was observed in 6 cases, recurrence was observed in 2 cases and 5 patients died. Superficial tumours therefore have a better prognosis in subjects under the age of 30. Invasive tumours are more frequent and often advanced, suggesting a marked potential for progression. Their prognosis depends on tumour stage, and is not correlated with age.