A case of achalasia of the cardia in a boy aged three months is described. This is the youngest case on record of a successful result following a modified Heller's operation in an infant. A biopsy specimen of the œsophageal muscle did not show any abnormalities in the myenteric plexus. These findings are discussed in the light of present concepts of the disease. The safety and reliability of surgery in these young infants are emphasised, making it the treatment of choice in pædiatric achalasi