Down syndrome is the most common chromosomal abnormality in humans. People affected by Down syndrome have high prevalence of autoimmune diseases. The most common autoimmune disease in this group of people is hypothyroidism. Hyperthyroidism occurs less frequent in this group of patients, but it is likely to be underestimated. We are presenting a case of Down syndrome and Graves’ disease. A 17-year-old Bahraini girl with Down syndrome and congenital heart disease, presented with history of weight loss within 6 months. Graves’ disease was confirmed based on laboratory and imaging results. Carbimazole 30 mg daily was started and increased to 40 mg daily. Adequate clinical and laboratory results were achieved. The association between Graves’ disease and Down syndrome is well known in medical practice and frequently reported in the literature. High clinical suspicion is crucial for early diagnosis and treatment. Different treatment modalities are available. Each modality carries different remission rate.