Abstract
In an epidemiological survey in Tromsø, northern Norway a prevalence of definite ankylosing spondylitis (AS) of between 1.1% and 1.4% was found (males: 1.9-2.2% and females: 0.3-0.6%). The ratio of male to female was between 3.9 and 6.1 in favour of the male sex. It was calculated that 6.7% of the B27 positive individuals had AS, and that 22.5% of the B27 positive subjects with back pain or stiffness suffered from AS.