Resection of primary tumour is the management of choice in patients with ectopic ACTH syndrome. However, tumours may remain unidentified or occult in spite of extensive efforts at trying to locate them. This can, therefore, pose a major management issue as uncontrolled hypercortisolaemia can lead to life-threatening infections. We present the case of a 66-year-old gentleman with ectopic ACTH syndrome from an occult primary tumour with multiple significant complications from hypercortisolaemia. Ectopic nature of his ACTH-dependent Cushing's syndrome was confirmed by non-suppression with high-dose dexamethasone suppression test and bilateral inferior petrosal sinus sampling. The primary ectopic source remained unidentified in spite of extensive anatomical and functional imaging studies, including CT scans and Dotatate-PET scan. Medical adrenolytic treatment at maximum tolerated doses failed to control his hypercortisolaemia, which led to recurrent intra-abdominal and pelvic abscesses, requiring multiple surgical interventions. Laparoscopic bilateral adrenalectomy was considered but decided against given concerns of technical difficulties due to recurrent intra-abdominal infections and his moribund state. Eventually, alcohol ablation of adrenal glands by retrograde adrenal vein approach was attempted, which resulted in biochemical remission of Cushing's syndrome. Our case emphasizes the importance of aggressive management of hypercortisolaemia in order to reduce the associated morbidity and mortality and also demonstrates that techniques like percutaneous adrenal ablation using a retrograde venous approach may be extremely helpful in patients who are otherwise unable to undergo bilateral adrenalectomy.