Urine cytology in addition to cystoscopy and transurethral resection is an integral part in diagnostic and follow-up of transitional carcinomas. The WHO-Classification of 2004 distinguishes between low grade and high grade tumours. Cytological diagnosis had to be adjusted to this new classification.Above all cytology has to detect high grade lesions in a reliable manner. The sensitivity for these lesions ranges between 85-95%. Well differentiated transitional cell carcinomas show marginal nuclear alterations compared to normal urothelial cells. Therefore the cytological low grade diagnosis is needless. Well differentiated papillary tumours can be detected with conventional cystoscopy in nearly 100 percent of all cases. This subtype of urothelial carcinomas is characterized by a very low rate of tumour progression despite a relevant rate of tumour recurrence. A negative cytology result combined with a cystoscopically proven papillary bladder tumour implies low grade disease with low risk of tumour progression.