In a study of 127 long-term psychiatric hospital patients perceived as difficult to treat, investigators used hierarchical grouping analysis to differentiate ten profile groups of patients. The groups are based on four dimensions or clusters of characteristics previously derived by factor analysis: withdrawn psychoticism, severe character pathology, suicidal-depressed behavior, and violence-agitation. The ten profile groups are described and are related to staff ratings of overall treatment difficulty, prognosis, sex, diagnosis, and other variables. The main conclusion is that treatment difficulty stems in large part from the compounding of different dimensions of severe psychopathology. Thus a pan-symptomatic group, with high scores on all four dimensions, ranks highest in overall treatment difficulty.