Autistic individuals experience higher rates of externalising and internalising symptoms that may vary with environmental factors. However, there is limited research on variation across settings that may highlight common factors with globally generalisable effects. Data were taken from two cohorts: a multinational European sample (n = 764; 453 autistic; 311 non-autistic; 6-30 years), and a South African sample (n = 100 non-autistic; 3-11 years). An exploratory factor analysis aggregated clinical (Verbal Comprehension and Perceptual Index), adaptive traits (Vineland Adaptive Behaviour Scale) and socio-economic variables (parental employment and education, home and family characteristics) in each cohort separately. With regression, we investigated the effect of these factors and autistic traits on internalising and externalising scores (measured with the Strengths and Difficulties Questionnaire). Cohorts showed similar four-factor structures (Person Characteristics, Family System, Parental and Material Resources). The 'Family System' factor captured family size and maternal factors and was associated with lower internalising and externalising symptoms in both cohorts. In the European cohort, high autistic traits reduced this effect; the opposite was found in the South Africa cohort. Our exploratory findings from two separate analyses represent consistent evidence that Family System is associated with internalising and externalising symptoms, with a context-specific impact in persons with high autism traits. [This article was written with the EU-AIMS LEAP Team.]