To determine which dimensions of psychopathology are associated with a greater liability to develop schizophrenia, the authors examined the case histories of 151 monozygotic probands from five twin studies. Proband twins from pairs concordant for schizophrenia had greater numbers of negative symptoms, poorer premorbid adjustment, fewer paranoid symptoms, and earlier ages at onset than probands from discordant pairs. In discriminant analyses, negative symptoms, premorbid social competence, and paranoid symptoms each contributed to the discrimination between concordant and discordant pairs. These results provide support for Strauss et al.'s suggestion that these three types of symptoms reflect three different functional processes in the development of schizophrenia.