Esophageal duplication cysts are rare embryonic malformations usually diagnosed in early childhood. They are often asymptomatic but they can cause dyspnoea, chest pain, or dysphagia or be complicated by intracystic hemorrhage, rupture, pulmonary or esophageal hemorrhage, and infection. Malignant transformation is an extremely rare event occurring within oesophageal cysts, adenocarcinoma being the most common histology. they are treated either surgically or endoscopically. We report a case of squamous cell carcinoma arising within an esophageal duplication cyst in adult complicated by perforation into thorax, treated with surgical resection.