Objective: Adrenal crisis (AC) is a life-threatening complication of adrenal insufficiency (AI). Here, we evaluated frequency, causes and risk factors of AC in patients with chronic AI.Methods: In a cross-sectional study, 883 patients with AI were contacted by mail. Five-hundred and twenty-six patients agreed to participate and received a disease-specific questionnaire.Results: Four-hundred and forty-four datasets were available for analysis (primary AI (PAI), n=254; secondary AI (SAI), n=190). Forty-two percent (PAI 47% and SAI 35%) reported at least one crisis. Three hundred and eighty-four AC in 6092 patient years were documented (frequency of 6.3 crises/100 patient years). Precipitating causes were mainly gastrointestinal infection and fever (45%) but also other stressful events (e.g. major pain, surgery, psychic distress, heat and pregnancy). Sudden onset of apparently unexplained AC was also reported (PAI 6.6% and SAI 12.7%). Patients with PAI reported more frequent emergency glucocorticoid administration (42.5 vs 28.4%, P=0.003). Crisis incidence was not influenced by educational status, body mass index, glucocorticoid dose, DHEA treatment, age at diagnosis, hypogonadism, hypothyroidism or GH deficiency. In PAI, patients with concomitant non-endocrine disease were at higher risk of crisis (odds ratio (OR)=2.02, 95% confidence interval (CI) 1.05–3.89, P=0.036). In SAI, female sex (OR=2.18, 95% CI 1.06–4.5, P=0.035) and diabetes insipidus (OR=2.71, 95% CI 1.22–5.99, P=0.014) were associated with higher crisis incidence.Conclusion: AC occurs in a substantial proportion of patients with chronic AI, mainly triggered by infectious disease. Only a limited number of risk factors suitable for targeting prevention of AC were identified. These findings indicate the need for new concepts of crisis prevention in patients with AI.