Objective: Primary adrenal insufficiency (PAI) is a rare disease with an inc reasing prevalence, which may be complicated by life-threatening adrena l crisis (AC). Good quality epidemiological data remain scarce. We performed a Belg ian survey to describe the aetiology, clinical characteristics, treatment regimens, comorbidities and frequency of AC in PAI. Methods: A nationwide multicentre study involving 10 major university ho spitals in Belgium collected data from adult patients with known PAI. Results: Two hundred patients were included in this survey. The median a ge at diagnosis was 38 years (IQR 25–48) with a higher female prevalence (F/M s ex ratio = 1.53). The median disease duration was 13 years (IQR 7–25). Autoimmune dis ease was the most common aetiology (62.5%) followed by bilateral adrenalectomy (2 3.5%) and genetic variations (8.5%). The majority (96%) of patients were treated with hydrocortisone at a mean daily dose of 24.5 ± 7.0 mg, whereas 87.5% of patient s also received fludrocortisone. About one-third of patients experienced one or more AC over the follow-up period, giving an incidence of 3.2 crises per 100 pat ient-years. There was no association between the incidence of AC and the maintenance dos e of hydrocortisone. As high as 27.5% of patients were hypertensive, 17.5% had diabe tes and 17.5% had a diagnosis of osteoporosis. Conclusion: This study provides the first information on the management of PAI in large clinical centres in Belgium, showing an increased frequency of postsurgical PAI, a nearly normal prevalence of several comorbidities and an overall good quality of care with a low incidence of adrenal crises, compared with data from other regi stries.