[Month of birth and prevalence of fibromyalgia].

We have studied the possible influence of season of birth on prevalence of fibromyalgia. Data from the Norwegian Fibromyalgia Association, where diagnosis is compulsory, were compared with mean figures for 1936-65 from the National Register of Births. Figures for 8,125 patients were correlated with figures for two million persons from the register. Unlike other musculoskeletal diseases, which are more prevalent in summerborn persons, and certain mental diseases, which are more prevalent in winterborn persons, no such association was found for fibromyalgia.