The similarities between high functioning autism (HFA) and schizotypal–schizoid personality disorder (SSPD) in terms of social cognition and interpersonal deficits may lead to confusion in symptom interpretation, and consequently result in misdiagnosis. Thus, this study aims to investigate differences in mentalizing with particular interest on the socio-cognitive and socio-affective dimensions. Three Advanced Theory of Mind (ToM) tests were applied in 35 patients with HFA, 30 patients with SSPD and 36 healthy controls. Individuals with HFA showed greater impairment and no dissociation between affective and cognitive ToM components. Conversely, SSPD individuals displayed less difficulties but greater impairments on the cognitive component. Beyond the replicability of ToM impairment in HFA individuals, our findings suggest more impaired cognitive ToM in SSPD participants which further support the sequence of mentalizing development build upon different chronological stages.