Necrosis, infarction, haemorrhage and cystic degeneration in thymoma are described mostly focally. Extensive cystic and necrotic degenerations are reported very rarely. A 38-year-old female patient was admitted to our hospital for right chest pain, cough and dyspnea of 3 months duration. Radiological investigations revealed a mass lesion 7x9 cm in diameter located in the anterior mediastinum without any calcifications, septation or mediastinal extension. During operation, a well encapsulated easily resectable large tumor tissue was observed. Pathological examination was suggestive of Type A thymoma which was challenging as regards the differential diagnosis of spindle cell atypical carcinoid. This rare entity was discussed with a literature survey.