Carcinoid tumour of the thymus is a rare condition, with less than a hundred cases reported in the literature. Diagnosis is complex as they are usually asymptomatic. We describe a case of a severe Cushing syndrome developed in a 51-year-old man. The diagnosis of a thymic carcinoid was established. Three years ago, the patient was treated by surgical resection of an anterior mediastinal mass. A massive tumour dissemination was detected by MIBG and CT image techniques. Both techniques are currently considered useful for this kind of diagnosis. ACTH secretion was detected immunohistochemically. Although the treatment with SMS-201-995 octreotide was effective in controlling the clinical symptoms, the patient died three months later with extensive metastases. The carcinoid tumours of the thymus associated to Cushing syndrome are aggressive tumours and usually produce local and distant metastases.