Allgrove's syndrome, i.e., achalasia, addisonianism, alacrima (OMIM 231550) is an autosomal recessive disorder recently associated with the AAAS gene coding for the Aladin protein. However, the pathophysiology of achalasia in Allgrove's syndrome remains obscure. Here we investigated the histopathology of the cardia in Allgrove's syndrome. Myectomy specimens from 10 children with Allgrove's syndrome and four normal cardia were studied by routine staining and by immunohistochemistry for the pan-neuronal marker PGP9.5, neuronal NO synthase, interstitial cells of Cajal, and CD3+ lymphocytes. In the normal cardia, myenteric ganglia, intramuscular nerve fibers, and interstitial cells of Cajal were numerous, whereas myenteric fibrosis and lymphocyte infiltrates were absent. In Allgrove's syndrome, fibrosis of the intermuscular plane was prevalent in all patients. Myenteric ganglia were absent, decreased, or apparently normal in 1 of 10, 8 of 10, and 1 of 10, respectively. Neuronal NO synthase was absent in 7 of 10 and decreased in 3 of 10, whereas interstitial cells of Cajal appeared normal in 7 of 10 and decreased in 3 of 10. Lymphocytes infiltrating the myenteric plexus were present in 6 of 10. Pyloromyectomy specimens available for six patients showed normal histopathologic features. In conclusion, the lack of neuronal NO synthase and fibrosis of the intermuscular plane can be linked to the defective cardia relaxation. Other features were less constant and may reflect the variability of disease expression and progression among patients with Allgrove's syndrome.