The main goal of this study was to investigate differences and similarities in general cognitive functioning between adults with schizophrenia and autism, because this has not been systematically investigated. We used a cross-sectional design to compare adults with schizophrenia (n = 27), with autism (n = 114) and a healthy control group (n = 30). Schizophrenia diagnoses were based on the Structured Clinical Interview for the DSM-IV Axis I (SCID-I) and behavioral symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS). Autism was diagnosed with a DSM-IV questionnaire for autism spectrum disorders and the Autistic Diagnostic Interview, revised version. The Wechsler Adult Intelligence Scale, third version (WAIS-III) was used to assess cognitive functions. All participants were between 18 and 65 years of age and had a minimum full scale intelligence of 80. Results showed that patients with schizophrenia scored significantly lower on processing speed than patients with autism and the healthy control group. Differences on other index scales were not found. In participants with schizophrenia a correlation was found between processing speed impairment and negative symptoms. Diagnosis could be predicted correctly with WAIS-III profile in 70.4% of the cases with schizophrenia compared to 56.7% of the healthy control group and 22.8% of the autism group. (C) 2014 Elsevier Ltd. All rights reserved.