As previously reported, gastroesophageal reflux (GER) is a frequent and severe medical complication of Cornelia de Lange syndrome (CDLS). The incidence of GER and the correlation between its presence and degree, and the clinical phenotype of CDLS (mild/classical according to Van Allen classification) were evaluated in a series of 43 patients. The pattern of presenting symptoms and their clinical evolution after medical or surgical treatment were also studied. A pathological GER was evident in 28/43 (65%) CDLS patients. The incidence of the complication was not significantly different in patients with classical (93.3%) vs. mild phenotype (82.3%), whereas a strong correlation was present between the degree of the esophageal damage and the clinical phenotype. A behavioral symptom (hyperactivity) was the most frequent sign associated with the condition (85%). Our data confirm the high occurrence of GER in CDLS patients, independently from the CDLS clinical phenotype. Regarding the severity of the esophageal lesions, a significant difference between the two clinical CDLS phenotypes was found. The evaluation of the presenting symptoms and of their evolution during the treatment emphasizes the importance of behavioral symptoms as major signs of esophageal damage in CDLS. © 2003 Wiley-Liss, Inc.