We investigated the length of time between the onset of pain symptoms and the surgical diagnosis of endometriosis in women from the UK and the USA. A total of 218 women with surgically confirmed disease, recruited through endometriosis self-help groups, completed a postal questionnaire. The mean +/- SD delay in diagnosis for women from the USA was 11.73 +/- 9.05 years, significantly higher than the equivalent delay of 7.96 +/- 7.92 years for women from the UK (P < 0.01). The stage of disease did not effect the length of time between the onset of symptoms and diagnosis. Therefore there is considerable delay in the diagnosis of endometriosis for women from both the UK and the USA. Efforts to reduce this delay are required to minimize the suffering of women with this disease.