We report on a 3-year-old boy with bilateral choanal atresia, hypoplastic nipples, and developmental delay who had been exposed to carbimazole in utero because of maternal Graves disease. His combination of abnormalities and facial appearance strongly resembles that of a previously reported child exposed to methimazole (which is the active metabolite of carbimazole) in utero. We suggest that this represents a rare but distinct syndrome of methimazole teratogenicity, probably related to first-trimester exposure. Recognition of such teratogenic effects is clearly important for genetic counselling and for management of subsequent pregnancies.