Cushing’s syndrome (CS) secondary to adrenocorticotropic hormone (ACTH) producing tumours is a severe condition with a challenging diagnosis. Ectopic ACTH-secretion often involves neuroendocrine tumours (NET) in the respiratory tract. ACTH-secreting small intestine neuro-endocrine tumours (siNET) are extremely rare entities barely reported in literature. This review is illustrated by the case of a 75-year old woman with fulminant ectopic CS caused by a ACTH-secreting metastatic siNET. Severe hypokalemia, fluid retention and refractory hypertension were the presenting symptoms. Basal and dynamic laboratory studies were diagnostic for ACTH-dependent CS. Extensive imaging studies of the pituitary and thorax-abdomen areas were normal, while [68Ga]Ga-DOTATATE PET-CT revealed increased small intestine uptake in the left iliac fossa. The hypercortisolism was well controlled with somatostatin analogues, after which a debulking resection of the tumour was performed. Pathological investigation confirmed a well-differentiated NET with sporadic ACTH immunostaining and post-operative treatment with somatostatin analogues was continued with favourable disease control.