Two (7%) out of 29 patients with chronic prostatitis were HLA B27 positive. They had roentgenological normal sacro-iliac joints. Two (7%) had sacro-iliitis as judged by radiological examination; one of them had never experienced low back pain. No patient had arthropathy in peripheral joints, ulcerative colitis, Crohn's disease, psoriasis or anterior uveitis. It was concluded that ankylosing spondylitis is rare in patients treated for chronic prostatitis.