Background: In schizophrenic psychoses, the normal sexual dimorphism of the brain has been shown to be disrupted or even reversed. Little is known, however, at what time point in emerging psychosis this occurs. We have therefore examined, if these alterations are already present in the at-risk mental state (ARMS) for psychosis and in first episode psychosis (FEP) patients. Methods: Data from 65 ARMS (48 (73.8%) male; age = 25.1 ± 6.32) and 50 FEP (37 (74%) male; age = 27 ± 6.56) patients were compared to those of 70 healthy controls (HC; 27 (38.6%) male; age = 26 ± 4.97). Structural T1-weighted images were acquired using a 3 Tesla magnetic resonance imaging (MRI) scanner. Linear mixed effects models were used to investigate whether subcortical brain volumes are dependent on sex. Results: We found men to have larger total brain volumes (p < 0.001), and smaller bilateral caudate (p = 0.008) and hippocampus volume (p < 0.001) than women across all three groups. Older subjects had more GM and WM volume than younger subjects. No significant sex × group interaction was found. Conclusions: In emerging psychosis there still seem to exist patterns of normal sexual dimorphism in total brain and caudate volume. The only structure affected by reversed sexual dimorphism was the hippocampus, with women showing larger volumes than men even in HC. Thus, we conclude that subcortical volumes may not be primarily affected by disrupted sexual dimorphism in emerging psychosis.