The study examines the genetic relationships between five major psychiatric disorders—schizophrenia, bipolar disorder, major depressive disorder, autism spectrum disorders (ASD), and attention-deficit/hyperactivity disorder (ADHD)—using genome-wide SNP data from the Psychiatric Genomics Consortium (PGC). The analysis employs univariate and bivariate methods to estimate genetic variation within and covariation between disorders. SNPs explained 17–29% of the variance in liability. High genetic correlations were observed between schizophrenia and bipolar disorder (0.68 ± 0.04 s.e.), moderate correlations between schizophrenia and major depressive disorder (0.43 ± 0.06 s.e.), bipolar disorder and major depressive disorder (0.47 ± 0.06 s.e.), and ADHD and major depressive disorder (0.32 ± 0.07 s.e.). Low genetic correlations were found between schizophrenia and ASD (0.16 ± 0.06 s.e.). These findings suggest shared genetic etiology among these disorders, providing empirical evidence for nosological integration and encouraging further investigation into common pathophysiologies. The results highlight the importance of common genetic variants in the etiology of these disorders and suggest that increasing sample sizes may lead to the discovery of additional genetic associations.The study examines the genetic relationships between five major psychiatric disorders—schizophrenia, bipolar disorder, major depressive disorder, autism spectrum disorders (ASD), and attention-deficit/hyperactivity disorder (ADHD)—using genome-wide SNP data from the Psychiatric Genomics Consortium (PGC). The analysis employs univariate and bivariate methods to estimate genetic variation within and covariation between disorders. SNPs explained 17–29% of the variance in liability. High genetic correlations were observed between schizophrenia and bipolar disorder (0.68 ± 0.04 s.e.), moderate correlations between schizophrenia and major depressive disorder (0.43 ± 0.06 s.e.), bipolar disorder and major depressive disorder (0.47 ± 0.06 s.e.), and ADHD and major depressive disorder (0.32 ± 0.07 s.e.). Low genetic correlations were found between schizophrenia and ASD (0.16 ± 0.06 s.e.). These findings suggest shared genetic etiology among these disorders, providing empirical evidence for nosological integration and encouraging further investigation into common pathophysiologies. The results highlight the importance of common genetic variants in the etiology of these disorders and suggest that increasing sample sizes may lead to the discovery of additional genetic associations.