There are no assessment and screening tools for Autism Spectrum Disorders (ASD) validated for the Portuguese population. The Social Communication Questionnaire (SCQ) is an useful screening tool of ASD diagnosis. The main objectives of our study were to produce a Portuguese version of the SCQ (SCQ-PF), study its internal consistency, sensitivity and specificity in order to evaluate its validity as a screening instrument for ASD. We also wanted to study the impact of intellectual disability and verbal impairment and other mental disorders on SCQ-PF psychometric properties. The study included 211 children and adolescents, aged 4–17, divided in three groups: ASD Group (n = 96), Other Mental Disorders Group (OMD) (n = 63) and No Mental Disorders (NMD) Group (n = 52). Parents or other primary caregiver provided information on the SCQ items. The SCQ-PF score was significantly higher in the ASD group than in the other groups (p < 0.001). As to internal consistency, Cronbach’s alpha was 87%. ASD subjects were distinguished from subjects without ASD (OMD and NMD Groups) and the area under the curve (AUC) was 0.897 (95% Confidence Interval: 0.852–0.943), for a cutoff of 14, which yielded the highest AUC, with values of sensitivity and specificity 0.76 and 0.93, respectively. These findings show that SCQ- PF with a cutoff of 14 is an acceptable and useful screening tool for ASD in the Portuguese population.