Schizotypal Personality Disorder (SPD) shares common genetic and biological substrates with schizophrenia, and patients with SPD have been reported to suffer both from specific cognitive impairments, and from a generalized cognitive dysfunction, similar to those found in schizophrenia. The aim of this cross-sectional, population-based study was to assess general cognitive functioning in adolescents with SPD. The Israeli Draft Board systematically assesses cognitive functioning and administers psychiatric screening in all 16-17-year-old males in the population. Of 341,511 males assessed, the cognitive test scores of adolescents with SPD (N = 326) were retrieved, and compared to the scores of adolescents diagnosed as suffering from schizophrenia (N = 901), and adolescents with no neurological or psychiatric diagnosis (controls, N = 293,820). Male adolescents with SPD or with schizophrenia scored lower on all measures compared to healthy individuals (effect sizes ranging from 0.6-0.88, all P < 0.001). The SPD patients scored significantly higher than the schizophrenia patients on the sub-tests of similarities and Ravens Progressive Matrices, tests that reflect abstract reasoning. On the sub-tests of arithmetic and instruction comprehension, tests that rely on concentration, SPD and schizophrenia patients' scores did not differ significantly from each other. These results might be interpreted to imply that a generalized cognitive impairment, in the presence of schizotypal personality traits and in the absence of psychosis, might be conceptualized as being the core of the schizotaxia syndrome. The greater impairment in abstract reasoning in the schizophrenia patients might be correlated with the psychotic symptoms that differentiate schizophrenia from SPD.