Background Endometriosis is an estrogen-dependent disease affecting 10% of females in which endometrial-like tissue grows outside the uterus, resulting in pain, infertility, and physical and psychosocial dysfunction. Prior research documenting diagnostic error reports a 6.7-year mean diagnostic delay. This study takes a patient-oriented approach and aims to complement prior research on diagnostic error by examining patient-reported experiences with misdiagnosis. Methods Data were part of a larger online survey comprising nonrandomly sampled patients with self-reported surgically confirmed endometriosis (n = 758). We examined patients' reports of misdiagnosis, to which healthcare professionals (HCPs) they attributed misdiagnosis, mean diagnostic delay, and endometriosis symptoms and physical sites predicting misdiagnosis reports. Results Mean reported diagnostic delay was 8.6 years. 75.2% of patients reported being misdiagnosed with another physical health (95.1%) and/or mental health problem (49.5%) and most frequently by gynecologists (53.2%) followed by general practitioners (34.4%). Higher odds of reporting a physical or mental health misdiagnosis was associated with reports of virtually all symptoms and endometriosis on the bladder, small bowel, pelvic sidewall, and rectum. Higher odds of reporting a physical health misdiagnosis was exclusively associated with reports of endometriosis on the appendix. Higher odds of reporting a mental health misdiagnosis was exclusively associated with reports of a younger symptom onset age; endometriosis on the diaphragm, large bowel, lung, and ureter; and comorbid adenomyosis diagnosis. Conclusions Endometriosis continues to present serious and complex diagnostic challenges. These findings corroborate previous objective investigations documenting endometriosis diagnostic error, establish the first patient-reported incidence, and further demonstrate value in including patients in diagnostic error research.