When is a baby’s fever high enough for me to call the doctor?

For an infant under 3 months old, a rectal temperature of 100.4F or above is cause for serious concern of infection. Go to an emergency room or doctor immediately. For babies from 3 months to 1 year old, a temperature of 100F is cause for calling a doctor for advice depending on your baby’s medical history. For children in general, temperatures between 100F and 104F may be frightening, but are probably a normal part of common illnesses.