Blue diaper syndrome, or Drummond's syndrome, is a very rare metabolic disorder that involves a defect in transport of the amino acid tryptophan from the intestine. Its inheritance is either X-linked or autosomal recessive.

The syndrome's name is derived from the fact that excess tryptophan breakdown causes formation of indigo blue and excretion into the urine, discoloring a diaper. Other symptoms include hypercalciuria with kidney stone formation, digestive symptoms, fever, and visual disturbances.

Treatment consists of a low tryptophan and low calcium diet.