Cytogenetic studies after short-term culture were performed on 120 consecutive adenocarcinomas of the prostate collected during a period of 12 months in one single centre. 46 out of 120 cases showed an abnormal karyotype including numerical and structural changes. Among the numerical changes (3946), loss of the Y chromosome was the most common numerical change followed by trisomy 7, monosomy 13, gain of a Y chromosome, trisomy 1, trisomy 14 and trisomy 5. Among the 12 cases with structural aberration, del(1)(q11) was the most common one followed by del(10)(q24), del(7)(q22), del(5)(p11) and del(4)(p11). In order to investigate whether there was a difference in the occurrence of numerical chromosome changes before and after culturing, we performed fluorescence in situ hybridization (FISH) with 7 and Y specific probes on single cell suspensions obtained after collagenase disaggregation of the tumor in 50 cases of prostate adenocarcinoma with cytogenetically normal karyotype, in 34 cases with abnormal karyotype and in 20 cases of benign prostatic hyperplasia (BHP). Cells with loss of Y chromosome and/or trisomy 7 were found to be present in adenocarcinomas with cytogenetically normal karyotype, in BPH as well as in some adenocarcinomas with structural chromosome changes.