Cysts within the oesophageal wall may represent inclusion cysts, retention cysts or developmental cysts. Foregut duplications are developmental anomalies, which occur as a result of abnormal canalization of the foregut during intrauterine life. Malignant transformation is an extremely rare event occurring within oesophageal cysts, adenocarcinoma being the most common histology. We report a case of squamous cell carcinoma arising within an oesophageal cyst affecting the upper third of the oesophagus. The malignant cyst was not amenable to primary surgical resection and hence was treated using chemo-radiotherapy. The treatment gave good disease control, at the expense of a high oesophageal stricture. Chemo-radiotherapy is an alternative treatment modality to achieve long-term disease control in squamous cell carcinoma complicating oesophageal foregut cyst when primary surgical resection is not possible.