There are many causes of polydipsia and polyuria in children, and the following are a few common diseases. 1, pituitary uremia: due to a variety of reasons caused by the pituitary gland anti-diuretic hormone secretion is reduced. The manifestation is obvious thirst, like cold drinks, often more than a few liters of water per day, urine light as water, urine specific gravity is low. The specific gravity of urine still does not increase in the water restriction test, and the application of antidiuretic hormone treatment is effective, which is the difference from nephrogenic enuresis. 2.Nephrogenic uremia: It is caused by the impaired reabsorption of water by renal tubules. It can occur soon after birth, but the infant’s thirst and polyuria are not easily detected; after 3 years of age, it shows polyhydramnios and polyuria, and is accompanied by growth retardation. 3. Diabetic polyhydramnios: caused by insufficient insulin secretion in the body. In addition to excessive drinking and urination, there are also signs of wasting and weakness. Check the increased blood sugar, positive urine sugar, insulin treatment is effective. 4.Vitamin D toxicity polydipsia and polyuria: There is a history of vitamin D overdose. In addition to polydipsia and polyuria, there are anorexia, vomiting and pallor. Urinary calcium and blood calcium are increased. 5, hyperparathyroidism caused by polyhydramnios: mostly due to hyperplasia of parathyroid glands. In addition to polydipsia and polyuria, there are poor appetite, vomiting, constipation, bradycardia and arrhythmia. High blood calcium, low blood phosphorus and high urine calcium. 6, habitual polydipsia and polyuria: this is non-pathological, no organic lesions, is due to feeding, life habits formed. As long as the amount of water consumed by the child is limited, the phenomenon of polyuria also changes. In addition, idiopathic hypercalcemia, aldosteronism, Fanconi syndrome, renal tubular acidosis, etc. can have the manifestation of polydipsia and polyuria, but they also have their corresponding manifestations, which can often be distinguished.