Schizophrenia is characterized by altered prefrontal activity and elevated striatal dopaminergic function. To investigate the relationship between these abnormalities in the prodromal phase of the illness, we combined functional Magnetic Resonance Imaging and (18)F-Dopa Positron Emission Tomography. When performing a verbal fluency task, subjects with an At-Risk Mental State showed greater activation in the inferior frontal cortex than controls. Striatal dopamine function was greater in the At-Risk group than in controls. Within the At-Risk group, but not the control group, there was a direct correlation between the degree of left inferior frontal activation and the level of striatal dopamine function. Altered prefrontal activation in subjects with an At-Risk Mental State for psychosis is related to elevated striatal dopamine function. These changes reflect an increased vulnerability to psychosis and predate the first episode of frank psychosis.