Adrenocortical carcinoma as a cause of Cushing's syndrome in a child is a rare occurrence. Functioning adrenal carcinomas are detected usually when they are small while non-functioning tumors are incidentally detected when they grow to a large size. Here we report a case of Cushing's syndrome due to large functioning adrenal carcinoma(>12 cm in size) in a 10 year old female child who presented with clinical features of Cushing's syndrome along with virilisation.A combination of biochemical laboratory reports along with radiological investigations followed by histopathology helped us to arrive at a proper diagnosis. The tumor was ressected and the patient showed clinical signs of improvement. However, the surgical margin showed invasion by the tumor making a likely possibility of recurrence in the near future.