Background/Aims: Endometriosis has a long diagnostic delay that is influenced by varying socio-economic and healthcare factors. In the Dutch situation, these factors are not yet identified. The aim of this study is to determine the length of the diagnostic delay of endometriosis in the Netherlands and to identify which variables affect this delay. Methods: A retrospective study among 139 patients diagnosed with endometriosis in a secondary care hospital with a specialized multidisciplinary endometriosis team. The diagnostic process was evaluated using a questionnaire-guided telephonic interview. Results: The median time interval from the onset of symptoms to diagnosis was 89 months or 7.4 years, divided in 7 months patient delay, 35 months general practitioner (GP) delay and 5 months gynecologist delay. Determinants for a longer diagnostic delay were young age at onset of symptoms, use of oral contraceptives or analgesics prescribed by GP, alternative diagnoses considered by the GP, and cyclic symptoms. Subfertility as presenting symptom resulted in faster diagnosis. Conclusion: This study shows that the time interval to the diagnosis of endometriosis is long and mainly consists of the period of time the woman consults her first line medical professional.