Ego-syntonic is a condition that relates to aspects of a person's behavior and attitude patterns that are consistent with the individual's basic personality and beliefs. The opposite of this is called ego-dystonic. In more straightforward terms this means that a person's outward behavior is consistent with their basic beliefs.
For instance, an ego-syntonic person who is generally kind and considerate of others is not likely to all of a sudden become violent and unpredictable. Changes in this condition can be a symptom of medical or psychological problems.