How high should I let my temperature get before I go to the er?

Depends... The number associated with a fever is irrelevant. Many people die with normal temperatures while countless others do just fine with crazy high temperatures. Your decision should be based on other symptoms or the risk of the source. Take tylenol (acetaminophen) or Ibuprofen for the fever and go to the er if you are concerned that your are deteriorating or more than just a simple fever.