Treatment with rosiglitazone has been associated with severe paradoxical HDL-c reductions. To our knowledge, there are very few reports of this reaction occurring when patients are treated without the combination of a fibrate. A case of severe HDL-c lowering in a patient treated with rosiglitazone without a fibrate is presented. The patient has been treated at a private practice clinic in southern Brazil. A 64-year-old woman with a 2-year history of type 2 diabetes mellitus was referred to her endocrinologist in June 2008. Rosiglitazone 4 mg q.d. was prescribed. Nine months later, the patient experienced a 90.90% decrease of her HDL-c levels. Rosiglitazone was withdrawn and the HDL-c returned to baseline. This paradoxical HDL-c reduction is a potentially severe adverse event. Patients prescribed rosiglitazone should have their HDL-c levels measured before and during therapy.