BACKGROUND Autoimmune thyroid disease (ATD) has been occasionally observed in patients with primary adrenal insufficiency (PAI). In contrast, less than 20 cases of comorbid PAI with ATD have been found in the English literature. One conceivable reason is difficulty in detecting latent PAI. OBJECTIVE Information of clinical presentation and diagnostics is sought to facilitate diagnosis of latent PAI. METHODS Latent PAI was pursued in 11 patients among 159 ATD patients. All of them were maintained in a euthyroid state. Except for one patient with nonrheumatic musculoskeletal symptoms, the other patients, who were asymptomatic in their daily lives, presented with recurrent nonspecific gastrointestinal symptoms or fatigue in stress-associated circumstances. Morning cortisol level <303 nmol/l was used as an inclusion criterion. Their basal adrenocorticotropic hormone levels were normal. The adrenal status was examined by a provocation test, either an insulin-induced hypoglycemia test or a 1-μg intravenous corticotrophin test. Eleven patients showed subnormal cortisol response. They were supplemented with hydrocortisone of doses ≤15 mg/day. After a few months of supplementation, PAI was confirmed by another provocation test. Three patients were excluded because of dissociation of two provocation tests. RESULTS Comorbid latent PAI with ATD was pursued from the symptoms stated above and proven by two provocation tests; it was found in 5% (8/159) of the patients. CONCLUSIONS When patients with ATD are troubled by recurrent stress-associated gastrointestinal or constitutional symptoms or nonrheumatic musculoskeletal symptoms which have remained unrelieved by adjustment of thyroid medication, these symptoms may be a manifestation of comorbid latent PAI. It is worth investigating such patients for latent PAI.