International CdLS Awareness Day is observed worldwide every second Saturday of May to educate the public about Cornelia de Lange syndrome (CdLS), a rare genetic disorder. The day was established to support patients and their families, advocate for better access to diagnosis and care, and promote research into this often misdiagnosed condition. CdLS is caused by mutations in one of seven different genes and can result in a variety of symptoms, including distinctive facial features, intellectual delays, and gastrointestinal problems. The syndrome was first described in 1933 by Dutch pediatrician Cornelia Catharina de Lange. Although there is no cure, treatment focuses on managing symptoms and improving quality of life through therapies and medical interventions. The incidence of CdLS is estimated to be about one in 10,000 live births, highlighting the importance of awareness and understanding of this condition.