Bilateral inferior petrosal sinus sampling for ACTH with corticotrophin releasing hormone stimulation has become an established test in differentiating pituitary Cushing's disease from Cushing's syndrome due to ectopic ACTH secretion. We report two patients with Cushing's disease who developed thromboembolic complications soon after inferior petrosal sinus sampling. We discuss the possible mechanisms leading to this complication in a syndrome in which thromboembolic complications are well recognized and highlight the need for consideration of prophylactic anticoagulation.