We investigated retrospectively 91 patients with prostatic carcinoma diagnosed cytologically between 1978 and 1979. Of the patients 57 had no metastases (M0) at presentation. The majority of the patients without metastases had well or moderately well differentiated carcinoma. Of 18 patients with poorly differentiated carcinoma 17 had metastases at presentation. The patients without metastases were left untreated, while those with metastases received active antitumor treatment. Local progression and/or development of metastases during surveillance occurred in 24 patients (42 per cent) and antitumor treatment was initiated. Mean observation time in the group untreated throughout observation was 47 months. Mean interval to progression in the patients treated subsequently was 31 months. In the surveillance group no difference in mean interval to progression, frequency of local progression, development of metastases or death rate of prostatic carcinoma was found when the patients with initially well and moderately well differentiated carcinoma were compared. Therefore, in our study initial cytological grade failed to predict a difference in progression in patients with well and moderately well differentiated prostatic carcinoma. Since almost all patients with poorly differentiated carcinoma had metastases at presentation a poor differentiation seems to predict a worse prognosis compared to well and moderately well differentiated tumors.