The incidence and prevalence of achalasia has been reported from a limited number of centers in the US, UK, Israel, Zimbabwe, Singapore, and New Zealand. With two exceptions, the studies have been retrospective. The incidence of the disease is about 0.5/10(5)/year with a prevalence of about 8/10(5) population. However, there appear to be striking international variations and also significant differences within countries. The disease occurs with equal frequency in men and women and is commoner with ageing. The appearance of the disease in the older age groups together with the lack of evidence for an autosomal recessive pattern of inheritance would suggest that environmental factors are important in the cause of the disease.