Two seemingly distinct psychiatric conditions may share more cognitive ground than previously understood. This finding challenges traditional diagnostic boundaries and suggests overlapping neural mechanisms underlying social difficulties in both disorders. The comprehensive comparison of 584 participants reveals that autistic individuals and those with schizophrenia spectrum disorders demonstrate remarkably similar impairments in social cognitive abilities compared to neurotypical controls. Both groups struggled equally with emotion recognition tasks and theory of mind assessments, suggesting common pathways in social information processing deficits. However, distinct cognitive profiles emerged when examining broader neurocognitive abilities. Individuals with schizophrenia spectrum disorders showed significantly greater impairments in processing speed, working memory, and both verbal and visual learning compared to autistic participants. These differences point to more widespread cognitive disruption in schizophrenia beyond social domains. The research team identified consistent correlations between social cognitive performance and general neurocognitive abilities across all groups, indicating that social difficulties may partially stem from underlying cognitive processing challenges. Notably, self-reported empathy measures predicted real-world social functioning regardless of diagnostic category. This transdiagnostic approach represents the largest systematic comparison of its kind, providing evidence for shared social cognitive vulnerabilities that transcend traditional diagnostic categories. The findings suggest that therapeutic interventions targeting social cognition might benefit from similar approaches across both conditions, while acknowledging that broader cognitive remediation may be more critical for schizophrenia spectrum disorders. These insights could reshape how clinicians conceptualize and treat social difficulties in neurodevelopmental and psychiatric conditions.