BACKGROUND/AIMS: A hypertensive lower esophageal sphincter (HLES) is an uncommon primary esophageal motility disorder that has been associated with chest pain and dysphagia, and the association of HLES and abnormal gastroesophageal reflux (GER) has not been well characterized. We tried to investigate the clinical characteristics of patients with HLES and we evaluated the relationship between HLES and GER. METHODS: Sixty-nine patients who were diagnosed as HLES between May 1995 and August 2004 were reviewed. Forty-four (64%) patients underwent 24-hour esophageal pH study and they were reviewed to evaluate the relationship between HLES and pathologic acid reflux (PAE). RESULTS: The most common presenting symptoms were non-cardiac chest pain and dysphagia. The mean value of resting lower esophageal sphincter pressure (LESP), the distal body amplitude and % relaxation of the lower esophageal sphincter were 60.0 mmHg, 93.8 mmHg and 98.9%, respectively. Seven (16%) of the forty-four patients who underwent 24-hour pH studies had PAE. The distal esophageal acid exposure (% pH<4) and the DeMeester score in patients with PAE did not show any correlation with the resting LESP. CONCLUSIONS: An abnormal GER was observed in some of the patients with HLES, and the distal esophageal acid exposure and DeMeester score did not show any correlation with the resting LESP for the patients with an abnormal GER. Ambulatory pH monitoring may be useful in HLES patients who present with reflux symptoms such as heartburn or chest pain.