OBJECTIVE: To investigate the detection rate and extent of high-grade prostatic intraepithelial neoplasia (HGPIN) and atypical glands (AG) suspicious for prostate cancer, and the cancer risk in subsequent biopsies, diagnosed by a first 24-core saturation biopsy, as although the optimum extent of biopsy is controversial there is a trend to increase the number of cores taken, and apart from detecting prostate cancer, identifying HGPIN and AG is associated with a greater risk of finding cancer in subsequent biopsies, thus warranting a closer follow-up. PATIENTS AND METHODS: The study included 100 men with consecutive first-time saturation biopsies; the indications for biopsy were an abnormal digital rectal examination and/or a serum prostate-specific antigen (PSA) level of >2.5 ng/mL. Each biopsy specimen was reviewed retrospectively by two pathologists to confirm the histological diagnosis. The number and percentage of cores positive for HGPIN, bilateral involvement and multifocality (HGPIN involving two or more cores) were recorded in each case. The presence of AG and cancer was also recorded. An extended (10-12 cores) repeat biopsy was available in 23 patients. RESULTS: The median (range) age and PSA level of the patients was 63 (41-80) years and 4.9 (1.5-67.0) ng/mL, respectively. Of the 100 patients, 34% had normal findings (benign prostatic tissue, BPT), 39% had cancer, 26% had HGPIN and cancer, 22% had HGPIN alone, and 5% had AG. Repeat biopsies were available in nine of the 22 (41%) patients with HGPIN, four of five with AG, and 10 of the 34 (29%) with BPT. The median (range) interval between the first and second biopsy was 13 (4-36) months. Prostate cancer was detected at the second biopsy in a third of patients with isolated HGPIN on the first biopsy, and one of the four with AG. None of the patients with BPT had cancer on re-biopsy. The cancer detection rate was significantly greater in patients with multifocal than in those with unifocal HGPIN (80% vs none, P = 0.010). The median number of cores and percentage of tissue involved by HGPIN was 3.5 (2-5) and 1.0 (0.5-1.2)%, respectively, in patients with cancer detected in repeat biopsies, compared to 1.0 (1-3) and 0.2 (0.2-0.6)% in patients without cancer on repeat biopsy (P = 0.023 and 0.015, respectively). CONCLUSION: Identifying multifocal HGPIN on first saturation biopsy is associated with an overall cancer detection rate of 80% on repeat 10-12-core biopsy. Although there were few patients, the detection of multifocal HGPIN warrants additional searches for concurrent invasive carcinoma by repeated biopsy. © 2007 The Authors.