Background: Diabetic ketoacidosis (DKA) is acute complication of diabetes mellitus. It is  commonly seen in type 1 diabetes mellitus and rarely also seen in type 2 diabetes mellitus. In more than fifty percent of cases precipitating factor is usually unrecognized. Case report: A 35 years women with type 1 diabetes mellitus presented with (DKA), with no apparent precipitating factor. Following initial correction of the DKA, persisting tachycardia, thyromegaly and thyroid functions confirmed diagnosis of thyrotoxicosis. Treatment with propranolol and carbimazole helped in the normalization of metabolic states. We hereby report a case of DKA precipitated by thyrotoxicosis. Conclusion: Thyrotoxicosis is known to destabilize diabetes control, it should be considered as one of the precipitating factor for diabetic ketoacidosis.