This review explores sex differences in the brain, focusing on gene expression, neuroanatomy, neurochemistry, cognition, and pathology. It highlights the importance of understanding these differences for developing personalized treatments for various diseases and understanding behavioral and pathological variations. The review discusses how sex chromosomes, hormones, and genetic factors influence brain development and function, and how these differences manifest in macroscopic and microscopic brain structures. It also examines sex differences in neurotransmitter systems, brain metabolism, and cognitive abilities, emphasizing the need for further research to fully comprehend these complexities. The review concludes by emphasizing the importance of considering both sexes equally in future studies to advance our understanding of sex-specific pathways and mechanisms in mental disorders.This review explores sex differences in the brain, focusing on gene expression, neuroanatomy, neurochemistry, cognition, and pathology. It highlights the importance of understanding these differences for developing personalized treatments for various diseases and understanding behavioral and pathological variations. The review discusses how sex chromosomes, hormones, and genetic factors influence brain development and function, and how these differences manifest in macroscopic and microscopic brain structures. It also examines sex differences in neurotransmitter systems, brain metabolism, and cognitive abilities, emphasizing the need for further research to fully comprehend these complexities. The review concludes by emphasizing the importance of considering both sexes equally in future studies to advance our understanding of sex-specific pathways and mechanisms in mental disorders.