Achalasia is the best known primary motility disorder of the esophagus. Dysphagia is the main symptom, intermittent at the beginning, but becoming more marked with evolution. Although some peculiarities are noted, they are not sufficiently characteristic to establish the diagnosis. Chest pain is often associated with dysphagia and may be the prominent complaint in the early stage of the disease. Dynamic investigations, mainly esophageal manometry, are needed for the diagnosis and follow-up after treatment. Three findings are commonly recorded: increase in lower esophageal sphincter pressure, lack of relaxation and absence of peristalsis, the latter being indispensable for the diagnosis of achalasia. On the basis of manometric findings, achalasia is easily differentiated from other primary motility disorders, i.e. diffuse esophageal spasm, nutcracker esophagus, but non-specific esophageal motility disorders are frequent. Manometry is also an objective method of assessing the effectiveness of treatment--i.e. surgical myotomy or balloon dilatation--of the lower esophageal sphincter.