Background Thirty years ago the highest multiple sclerosis (MS) prevalence rates in the world were recorded in northern Scotland. We did a prevalence study in Aberdeen, Orkney and Shetland to calculate age gender specific prevalence rates, compare rates between areas and over time, by subtype, diagnostic criteria and socioeconomic group.

Methods We used medical and laboratory records to identify prevalent MS patients on 24 September 2009. Questionnaires and records were used to verify diagnoses (using Poser and McDonald criteria) and disability status. Rates were standardised to the Scottish population.

Results 590 patients were found (Aberdeen 442, Orkney 82 and Shetland 66). Mean age was 53 years (SD±13) and the male to female ratio was 1:2.55 (95% CI 2.26 to 2.89). The standardised prevalence rates per 100 000 in the combined area were 248 (95% CI 244 to 252), Orkney 402 (95% CI 313 to 487), Shetland 295 (95% CI 225 to 366) and Aberdeen 229 (95% CI 208 to 249). Orkney and Shetland rates increased. 50% had relapse remitting disease. 45% had significant disability (EDSS≥6). Prevalence using Poser definite criteria was 219 (95% CI 215 to 224) and for McDonald 202 (95% CI 198 to 206). The prevalence was lowest in the bottom socioeconomic group.

Conclusion The prevalence of MS has increased in the study area since the 1980s. This may reflect methodological differences in previous studies, improved diagnostic methods, improved survival or rising incidence. Orkney has the highest prevalence rate in the world.