SummaryBackgroundAn adrenal crisis (AC) is a potential life‐threatening event in patients with adrenal insufficiency (AI). This study aims to determine the incidence, causes, and risk factors of AC in AI.MethodsPatients with AI diagnosed and treated at the University Medical Center Utrecht for the past 30 years were identified, and all medical records were assessed by two independent investigators. The observed frequency of AC was determined as incidence rate, calculated as the number of AC divided by person‐years (PY). In addition, precipitating factors and risk factors were assessed.ResultsWe observed an incidence rate of 5·2 AC (95% CI 4·3–6·3) per 100 PY in primary adrenal insufficiency (PAI, a total of 111 patients), and 3·6 AC (95% CI 3·1–4·1) per 100 PY in secondary adrenal insufficiency (SAI a total of 319 patients). Patients with an established diagnosis of tertiary (glucocorticoid‐induced) adrenal insufficiency (a total of 28 patients) had 15·1 AC (95% CI 11·0–19·9) per 100 PY. The most important risk factor was the existence of comorbidity. Gastro‐enteritis and other infections were the most common precipitating factors for AC.ConclusionAC still occurs relatively frequent in patients with AI, mostly precipitated by infections and particularly in patients with high comorbidity. This should be taken into account in the education and follow‐up of patients with AI.