Abstract Disclosure: L. Javed: None. A. Rehan: None. L. Hashim: None. J. Lim: None. Introduction: Diabetic ketoacidosis (DKA) is a common cause of hospitalization and readmission in patients with diabetes mellitus. Etiologies are generally due to medication non-adherence, trauma, infection, or other precipitating illness. In approximately 10% of DKA cases, no discernible precipitating cause can be determined. The word catamenial is derived from a Greek word meaning monthly. It is used to describe the monthly occurrence of menstruation. Catamenial hyperglycemia is a phenomenon in which blood glucose levels change with the different phases in the menstrual cycle. This can precipitate recurrent, unexplained episodes of DKA. Here, we present a similar case. Case description:A 19-year-old woman with type 1 diabetes, gastroparesis, hypertension, dysmenorrhea and cyclical vomiting disorder presented with unrelenting nausea and vomiting for one day. Other symptoms included abdominal & chest pain that the patient attributed to premenstrual symptoms. She is afebrile, doesn’t have any other symptoms of infection and no recent sick contacts. She is compliant with her home insulin regimen of Insulin detemir 20 units BID and pre meal 8 units insulin aspart. Further interrogation reveals she has regular menstrual cycles and has been hospitalized three times in the last three months due to DKA coinciding with premenstrual symptoms, specifically severe abdominal pain and vomiting, typically starting five days before the onset of her menstrual cycle. She is hemodynamically stable and physical exam is significant for mid epigastric tenderness. Significant labs: WBC 16.52 (N<11 K/mm3), glucose 457 mg/dl, anion gap 23, K 4.1 (mmol/L), bicarbonate 18 (≥19 mmol/L), lactate 3.2 (N ≤ 1.9 mmol/L), beta hydroxybutyarate 4.0 (N ≤ 0.27 mmol/L), trop T 6 (N<10 ng/L), BHCG negative . Hba1c a month ago was 9.6%. Infectious work up was negative. EKG showed no signs of ischemia. She was treated per DKA protocol which results in resolution of symptoms and normalization of labs. Since no other precipitating factors for DKA are identified, and her symptoms corresponded with her menstrual periods, she is given a diagnosis of Catamenial DKA and scheduled for regular follow up in endocrinology clinic. Conclusion: This case highlights the importance of considering the association betweenmenstrual cycle phases and blood sugar levels as a possible trigger, underscoring the role of a thorough menstrual history in patients presenting with DKA. The impact of menstrual cycle fluctuations on glycemic control varies among patients however glucose profiles seem to be consistent across cycles for each individual woman. This highlights the need for personalized management strategies including patient education and adjustment of insulin during these periods. Addressing this adequately will improve overall glycemic control, reduce hospitalizations, and help improve the quality of life. Presentation: 6/1/2024