This study estimates the genetic relationships between five psychiatric disorders—schizophrenia, bipolar disorder, major depressive disorder, autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD)—using genome-wide SNP data from the Psychiatric Genomics Consortium (PGC). The results show that genetic variation contributes to the liability of these disorders, with common SNPs explaining 17–29% of the variance. Genetic correlations were calculated between the disorders, revealing high correlations between schizophrenia and bipolar disorder (0.68), moderate between schizophrenia and major depressive disorder (0.43), bipolar disorder and major depressive disorder (0.47), and ADHD and major depressive disorder (0.32). Lower correlations were found between schizophrenia and ASD (0.16), and no significant correlations were observed between other disorder pairs or between psychiatric disorders and Crohn's disease. The study also found that common genetic variants contribute to both childhood-onset disorders (ASD and ADHD) and disorders typically diagnosed after childhood (schizophrenia, bipolar disorder, and major depressive disorder), though the sharing of common variants between these groups is modest. The results suggest that schizophrenia, bipolar disorder, and major depressive disorder share genetic etiology, and that the genetic overlap between these disorders is consistent with polygenic profiles and previous family studies. The study highlights the importance of genetic factors in psychiatric disorders and provides empirical evidence of shared genetic etiology. It also underscores the need for further research into the common pathophysiology of related disorders. The findings have implications for the classification and understanding of psychiatric disorders, suggesting that they may be part of a broader genetic spectrum. The study also notes that the genetic correlations observed may be influenced by factors such as misclassification of disorders and population stratification. Overall, the study provides valuable insights into the genetic architecture of psychiatric disorders and their potential for shared genetic risk factors.This study estimates the genetic relationships between five psychiatric disorders—schizophrenia, bipolar disorder, major depressive disorder, autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD)—using genome-wide SNP data from the Psychiatric Genomics Consortium (PGC). The results show that genetic variation contributes to the liability of these disorders, with common SNPs explaining 17–29% of the variance. Genetic correlations were calculated between the disorders, revealing high correlations between schizophrenia and bipolar disorder (0.68), moderate between schizophrenia and major depressive disorder (0.43), bipolar disorder and major depressive disorder (0.47), and ADHD and major depressive disorder (0.32). Lower correlations were found between schizophrenia and ASD (0.16), and no significant correlations were observed between other disorder pairs or between psychiatric disorders and Crohn's disease. The study also found that common genetic variants contribute to both childhood-onset disorders (ASD and ADHD) and disorders typically diagnosed after childhood (schizophrenia, bipolar disorder, and major depressive disorder), though the sharing of common variants between these groups is modest. The results suggest that schizophrenia, bipolar disorder, and major depressive disorder share genetic etiology, and that the genetic overlap between these disorders is consistent with polygenic profiles and previous family studies. The study highlights the importance of genetic factors in psychiatric disorders and provides empirical evidence of shared genetic etiology. It also underscores the need for further research into the common pathophysiology of related disorders. The findings have implications for the classification and understanding of psychiatric disorders, suggesting that they may be part of a broader genetic spectrum. The study also notes that the genetic correlations observed may be influenced by factors such as misclassification of disorders and population stratification. Overall, the study provides valuable insights into the genetic architecture of psychiatric disorders and their potential for shared genetic risk factors.