The pain of teething in infants has been recognized for 5000 years. Primary (“baby”) teeth eruption begins around 6 months and extends to 24–30 months, an age when infections and other causes of distress are very common. Sore gums, drooling, and biting behavior are well-established local (oral) signs and symptoms of teething. Many parents, and even health care providers, also believe that systemic symptoms like fever and diarrhea are caused by teething. The best-designed observational studies have involved longitudinal follow-up of infants with frequent, intensive measurement of new tooth eruption and of new signs and symptoms, but blinding of observers is difficult. The most rigorous of these observational studies show increased irritability and disturbed sleep associated with teething, but not diarrhea or true fever, although some have shown higher average temperatures within the normal range.