Abstract We present the case of a 16-year-old male with Cushing's disease (CD) who faced diagnostic challenges due to the absence of an image on magnetic resonance imaging (MRI) of the sellar region. Despite undergoing surgical intervention, clinical and biochemical cure was not achieved. Inferior petrosal sinus sampling (IPSS) was performed for the first time in the country within this age group. The procedure proceeded without complications, leading to the establishment of a CD diagnosis. Pharmacological treatment with ketoconazole was initiated as a bridge therapy until definitive treatment; however, the patient did not tolerate ketoconazole. Due to an underdeveloped sphenoidal sinus, surgery was deemed inappropriate, and radiotherapy was administered. Performing PSC is crucial, as it is established as the gold standard for differentiating etiologies when other diagnostic studies are inconclusive. Keywords: Cushing's Syndrome, Cushing's Disease, Petrose Sinus Catheterization.