Records of 34 hyperventilating children aged 18 years or younger seen at the Mayo Clinic over a 25-year period were reviewed. Five different clinical subtypes were identified. Evaluation and treatment varied considerably. At follow-up, 40% were still hyperventilating as adults, and many had signs and symptoms of chronic anxiety. Hyperventilation in childhood can be a signal that the child is experiencing severe anxiety, which may persist into adulthood.