Aim Patients with achalasia may have a thicker muscularis propria layer than normal subjects. The aim of our study was to determine the prevalence of increased muscle thickness in patients with achalasia measured by endoscopic ultrasonography (EUS) and evaluation of its relationship with disease characteristics. Methods For a 1-year period we studied 16 nonachalsia patients and 16 consecutive achalasia patients before pneumatic dilation. Esophageal muscle thickness was measured at the esophagogastric junction (EGJ), and 5 and 10 cm from the EGJ. Patients' symptom scores and their relief were evaluated 1, 3 and 6 months after treatment. Results Nearly all patients with well-defined achalasia revealed an increase in the muscle thickness relative to controls. There was a correlation between the thickness at 5 and 10 cm above the EGJ and the age of patients with achalasia. Symptom scores, mean lower esophageal pressure, disease duration and response to treatment were not correlated with the rate of increase in muscle thickness. Conclusion Increased esophageal muscle thickness by EUS is likely to be an important marker of achalasia. Sex, symptom score, mean LES pressure, duration of disease and response to treatment were not correlated with muscularis layer thickness.