What is the current diet of women with endometriosis, in terms of adherence to dietary guidelines and use of diets, and what are the perceived effects of dietary modifications? In this online explorative observational study, the Dutch Healthy Diet 2015 index (DHD-15) and quality of life (QoL) with the Endometriosis Health Profile-30 questionnaire (EHP-30) were used to assess diet quality. The questionnaires were completed by 157 participants. Many participants made one or more dietary adaptations for their endometriosis, in the form of a specific diet (46.5%), with the use of dietary supplements (56.1%), with other dietary adjustments (64.3%), or all. Endometriosis patients had a significantly lower DHD-15 score, indicating a lower diet quality than a healthy reference group (P = 0.004). In the endometriosis group, diet users had a significantly higher total DHD-15 score than non-diet users (P < 0.0001). Diet quality was not correlated with QoL (Pearson's r = –0.010, P = 0.904). Many specific dietary adjustments (71.3%), however, were reported to reduce endometriosis pain-related symptoms. The removal of gluten, dairy or soy, as well as the addition of vegetables, showed the greatest perceived reductions of symptoms in participants. Although no specific dietary adjustment was found to increase QoL, endometriosis patients do feel that dietary adjustments have a beneficial effect on their symptoms. Therefore, more research is needed to gain evidence about the specific effects of nutrients on endometriosis symptoms. [ABSTRACT FROM AUTHOR]