: Endometriosis is a hormone-dependent chronic inflammatory disease with serious reproductive and general health consequences. It is viewed as a multifactorial problem, consisting of matters related to altered immunity and genetics. In this study, we determined the correlation between endometriosis and allergic and autoimmune diseases in patients at reproductive age. : Online surveys distributed through websites related to gynecological problems. The questionnaire was composed of 63 single and multiple-choice questions concerning the course of endometriosis, diet, and allergic and autoimmune diseases. The obtained data were assessed using statistical tests. : 501 female patients (mean age 31.1 SD = 6.8) were included in the study. The control group ( = 155) consisted of healthy females, whereas the study group ( = 346) consisted of female patients with endometriosis; each group was subdivided according to allergy status. There were statistically significant differences between groups for the following: positive family history of endometriosis ( = 0.0002), onset of allergic symptoms ( = 0.0003), frequency and duration of abdominal pain ( = 0.00625), and defecation disorders ( = 0.0006). Asthma was less common in the study group ( = 0.00611). The group of patients with endometriosis and allergies had a high median of consumption of red meat ( = 0.0143), fish ( = 0.0016), and dairy products ( = 0.0001). : Endometriosis did not affect autoimmune diseases and their courses. Patients with diagnosed endometriosis presented allergy symptoms much earlier than the healthy patients. The consumption of dietary products such as soya products, red meat, and alcohol had an influence on the occurrence of endometriosis.