Endometriosis is a complex disease that affects a large number of women of reproductive age and imposes a significant burden on patients and society. The aim of this study was to evaluate diagnosis, comorbidities, healthcare resource use, treatment patterns, costs and quality of life of women with endometriosis seen in a Belgian tertiary care centre. A total of 134 patients were included in a prospective questionnaire-based cost-of-illness study. Patients were diagnosed after a median delay of 2 years after onset of symptoms. Almost all patients reported having at least one comorbidity. Total annual costs per patient were €9872 (95% confidence interval €7930–11,870), with costs of productivity loss representing 75% of total costs. Hospitalizations, surgeries, infertility treatments, pain and anxiety increased total costs significantly ( P ⩽ 0.001). Patients generated an average of 0.82 QaLY over a 1-year time horizon. This study showed that direct and indirect costs attributable to endometriosis-associated symptoms are substantial. Earlier diagnosis and cost-effective treatment of endometriosis may decrease productivity loss, quality of life impairment and healthcare consumption and consequently reduce total costs to patients and society. Endometriosis is a complex disease that affects a large number of women of reproductive age and imposes a significant burden on patients and society. The aim of this study was to evaluate diagnosis, comorbidities, healthcare resource use, treatment patterns, costs and quality of life of women with endometriosis seen in a Belgian hospital centre that specializes in endometriosis. A total of 134 patients were included in a prospective questionnaire-based cost-of-illness study. Patients were diagnosed after a median delay of 2 years after onset of symptoms. Almost all patients reported having at least one other disease in addition to endometriosis. Total annual costs per patient were €9872, with costs of productivity loss representing 75% of total costs. Hospitalizations, ...