OBJECTIVE: Many schizophrenia patients remain undiagnosed and untreated for long periods of time. It has been suggested that untreated psychosis may have deleterious neurotoxic effects. However, studies examining the correlates of untreated initial psychosis duration have been mixed. Previous MRI studies have reported no significant correlations between duration of untreated initial psychosis and brain volumes but have not examined specific brain regions that may be most susceptible to neuronal damage. METHOD: The authors investigated the relationship between duration of untreated initial psychosis and hippocampus morphology in 105 patients with first-episode DSM-IV schizophrenia spectrum disorders. High-resolution MRI-based hippocampal volume measurements were obtained by using a semiautomated artificial neural network method. RESULTS: There were no significant associations between hippocampal volumes and duration of untreated initial psychosis. When the patient group was split around the median duration of untreated initial psychosis (13 weeks), there were again no significant differences in left, right, or total hippocampal volume between groups. CONCLUSIONS: These findings do not support the hypothesis that psychosis is neurotoxic or that delaying antipsychotic drug treatment results in reduced hippocampal volumes.