Background <p>Hyperemesis gravidarum is a pregnancy-related condition marked by intractable nausea and vomiting, often resulting in volume depletion, electrolyte abnormalities, and weight loss. While the typical biochemical profile includes hypochloremic, hypokalemic metabolic alkalosis, ketoacidosis is uncommon and typically associated with prolonged starvation. Although thyrotoxicosis has been reported in association with HG, the concurrent occurrence of ketoacidosis is exceedingly rare, particularly in the absence of an identifiable precipitating factor.</p> Case presentation <p>We describe the case of a 31-year-old woman at 11 weeks and 6 days of gestation who presented with a three-week history of severe nausea, vomiting, fatigue, syncope, and oral intolerance. Laboratory evaluation revealed hypokalemia, hypochloremia, elevated anion gap metabolic acidosis with ketosis, and thyrotoxicosis, in the absence of any trigger, e.g: concurrent infection, surgical complications, or diabetes. The patient was managed with intravenous fluid resuscitation, electrolyte repletion, bicarbonate therapy, antiemetics, and thromboprophylaxis, with gradual clinical improvement of metabolic derangements and self-resolution of thyroid abnormality by week 14 of gestation.</p> Conclusions <p>This case highlights an atypical presentation of hyperemesis gravidarum complicated by starvation ketoacidosis and thyrotoxicosis in the first trimester in the absence of precipitating factors. Early recognition and prompt supportive management are critical to prevent maternal and fetal morbidity in such rare presentations.</p>