Down's syndrome or trisomy 21 is a genetic disorder caused by presence of all or a part of a third copy of chromosome 21. Keratoconus occurs in up to 15% of the adult population with Down's syndrome. There is a close consortium between trisomy 21 and keratoconus (a conical ectatic protrusion of the cornea), and children with Down's syndrome are also susceptible to developing thyroid disease, including hypothyroidism and thyrotoxicosis with exophthalmos. The authors describe a case report on acute corneal hydrops with congenital cerulean cataract in a patient with Down's syndrome with hypothyroidism having bilateral advanced keratoconus. As per the detailed literature review, this is the first case of Down's syndrome with hypothyroidism presenting with acute corneal hydrops.