Epidemiological studies of adenomyosis are difficult to interpret because the diagnostic criteria vary so widely that the disease may be easily over-diagnosed. This would severely hamper any attempt to define incidence and prevalence of the condition and the related risk factors, and would limit the possibility of clarifying to what extent adenomyosis contributes to clinical symptoms. There is a need for stringent and widely accepted diagnostic criteria in order to define not only the presence of adenomyosis but also depth of penetration and degree of spread of foci. Moreover, the evidence available on epidemiological characteristics of women with adenomyosis is greatly biased by the type of population studied, i.e. women undergoing hysterectomy. Therefore, a consensus on non-surgical diagnostic criteria at transvaginal ultrasonography and MRI is indispensable and urgently needed in order to be able to conduct epidemiological studies in women younger than those evaluated until now.