Research into psychosis proneness has established the Chapman Psychosis Proneness Scales (CPPS), certain personality disorders, certain response patterns on the MMPI-2, and social withdrawal as being valid indicators of liability. The current study extends our understanding of premorbid indicators of schizophrenia-related psychosis (SRP) by examining whether individuals identified as hypothetically psychosis prone (HPP) by virtue of their CPPS scores also show differences on other premorbid indicators of SRP. Results indicate that HPP individuals evidence more deviancy in the schizophrenic direction. By providing additional construct validity for the CPPS and other endophenotypic indicators of premorbid processes, strategies for understanding the development of SRP are enhanced.