Abstract The principal aim of a population-based cross-sectional survey was to generate information on the lifetime occurrence of prostatitis in Finnish men and their exposure to the disease, and also on the influence of prostatitis-related fears and disturbances on their sexual life. A second aim was to develop and clinically validate a new diagnostic tool for differential diagnosis between the forms of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), especially between patients belonging to categories IIIA and IIIB in the new NIH (National Institutes of Health) clinical classification. Altogether 1832 men out of 2500 aged 20–59 years chosen randomly from the two most northerly provinces of Finland (Oulu and Lapland) participated in the epidemiological study, a response rate of 75%. The overall lifetime prevalence of prostatitis was 14.2%. The risk of having had the disease increased with age, being 1.7 times greater in the men aged 40–49 years than in those aged 20–39 years, and 3.1 times greater in those aged 50–59 years. More than a quarter of the 261 men who had or had had prostatitis symptoms (27%) suffered from them at least once a year, while 16% suffered from chronic prostatitis symptoms throughout the year. 63% of the men with prostatitis had their worst symptoms during the wintertime (November–march). 17% of the men with chronic prostatitis reported a constant fear of undetected prostate cancer. Erectile dysfunction was reported by 43% of the symptomatic men and decreased libido by 24%. Self-assessment of personality showed that the men with prostatitis were more often busy and nervous and had a meticulous attitude to life and problems than were the non-symptomatic men. 197 patients with chronic prostatitis/chronic pelvic pain syndrome participated in three clinical case-control studies during the years 1995–2000, at Oulu University Hospital, the District Hospital of Oulainen and Seinäjoki Central Hospital. The first prostatic tissue pressure measurement (PTPM) study included 34 patients and 9 controls. A novel method was developed to measure intraprostatic tissue pressure with a Stryker® intracompartmental pressure monitor. The PTPM showed a clear increase (p < 0.001) in the patients with symptoms of prostatitis and benign prostatic enlargement (BPE) relative to the controls and the patients with BPE but without pain symptoms. The second PTPM study included 42 patients with chronic prostatitis symptoms without significant BPE and 12 new controls. Significantly higher pressure readings (p < 0.001) were recorded at all three measurement points in the patients than in the controls. 48 new patients and 12 new controls were enrolled for the third PTPM study, the purpose of which was to confirm the results of the previous ones and to compare the prostatic tissue pressures of two clinical groups (IIIA and IIIB). The prostatic tissue pressure was again significantly higher in the patients with chronic prostatitis symptoms than in the controls (p < 0.001). An interesting finding was that prostatitis patients belonging to clinical category IIIA had significantly higher tissue pressures (p < 0.01) than those in category IIIB, probably reflecting more severe inflammation in the prostatic tissue. This new PTPM method provides a more precise and/or exact tool for differential diagnosis between the forms of pelvic pain and CP/CPPS.