This study examined whether street homelessness, sheltered homelessness, and the severity of psychological symptoms predicted non-violent and violent crime among 207 mentally ill participants who were homeless at baseline. Participants were interviewed at 9 time points over 4 years. Hierarchical linear modeling (HLM) was used to examine whether changes in homelessness status and symptom severity predicted changes in criminal activity over time. Results indicated that homelessness both on the streets and in shelters and psychological symptom severity predicted increases in non-violent crime. Sheltered homelessness and symptom severity predicted increases in violent crime, although street homelessness did not. A separate mediational analysis with 181 participants showed that the relationship between diagnosis of a psychotic disorder and both non-violent and violent criminal activity was partially mediated through the severity of psychotic symptoms. Implications for research and intervention are discussed.