Gastroenteritis is usually caused by microbial infections, but can also be caused by chemical poisons or drugs. Typical clinical manifestations are diarrhea, nausea, vomiting and abdominal pain. Viral infections are the most common cause of gastroenteritis. There are several viruses that can cause gastroenteritis, the most common being rotavirus, followed by norovirus, astrovirus and enteroadenovirus. The most important treatment for gastroenteritis is hydration and electrolytes. Patients usually only need to rest and drink adequate amounts of water (e.g., oral rehydration salt solution). Even patients who are vomiting should drink as much water as possible. Nursing infants should continue to nurse. Carbonated beverages, tea, sports drinks, caffeinated beverages and fruit juices are not suitable for rehydration. If vomiting or diarrhea is prolonged or severe dehydration is present, intravenous rehydration may be necessary. Antiemetics may be added in cases of severe vomiting. If the diarrhea lasts longer than 24 to 48 hours and there is no indication of a more serious bacterial infection, antidiarrheal medication may be added. Self-administration of antiemetics and antidiarrheal medications is not usually recommended for children. Because antibiotics may cause diarrhea or promote the growth of drug-resistant bacteria, antibiotics are usually not recommended even if the causative agent of gastroenteritis is known. However, antibiotics may be used for certain pathogenic bacterial (e.g., Campylobacter, Shigella, Vibrio cholerae, etc.) infections or if the patient has traveler’s diarrhea. For gastroenteritis due to viral infections, antibiotics are not effective. Anti-parasitic drugs are required for gastroenteritis due to parasitic infections. Gastroenteritis in children progresses rapidly and electrolyte disturbance is a very dangerous problem, so it should not be taken lightly and should be treated promptly by a doctor.