DNA ploidy status of tumour cells is becoming a part of patient's record, because it brings an objective assessment of diagnostic and prognostic significance. DNA ploidy status in diagnosis--DNA ploidy status of some tumour types can be used as an adjunct to cytologic or histologic examination and provide an additional diagnostic information. For example, small cell lung carcinoma cells may be difficult to differentiate from cells of other benign neuroendocrine tumours. By computing the DNA malignancy grade, as defined by Bocking A. et al., it was possible to distinguish levels of malignancy among neuroendocrine tumours. Thus we were able to demonstrate that typical carcinoids may be differentiated from small cell carcinomas and atypical carcinoids. DNA ploidy status in prognosis--A large number of studies strongly support a correlation between DNA ploidy patterns and clinical course of malignant tumours. However, the prognostic value of DNA ploidy status has to be evaluated in relation to conventional clinico-pathologic characteristics, by multivariate analysis in order to demonstrate its independent contribution. For example, we demonstrated, in a prospective study of 211 colorectal adenocarcinomas, that ploidy status was an independent predictor of prognosis only in the early stages of the disease (Dukes' A, B, C), but not when advanced stages-(Dukes' D) were considered. In conclusion, DNA ploidy status may be used as an important objective parameter either in diagnosis or in prognosis, complementary to the traditional clinico-pathological characteristics.