Gastrointestinal symptoms and their relation to physical and mental aspects in adults with an autism spectrum disorder (ASD) are poorly understood, despite their high prevalence. Therefore, the aim of this study is to examine psychological, behavioural and biological factors associated with gastrointestinal symptoms in adults with ASD (traits). We included 31,185 adults from the Lifelines Study. Using multivariable logistic regression, we analysed the association between gastrointestinal symptoms and psychological, behavioural (questionnaire-assessed) and physically measured biological factors in adults with ASD (n = 309), without ASD (n = 30,876), and in the quartiles with highest (n = 7783) and lowest (n = 7783) Autism Spectrum Quotient-10 sum scores. In the ASD-group, gastrointestinal symptoms were associated with psychiatric comorbidity (odds ratio: 2.71, 95% confidence interval: 1.51-4.85), more stress (odds ratio: 1.15, 95% confidence interval: 1.06-1.26), and worse perceived health (odds ratio: 2.32, 95% confidence interval: 1.62-3.34). In the quartile with the highest Autism Spectrum Quotient-10 sum scores, gastrointestinal symptoms were also associated with these psychological factors, and with less physical activity (odds ratio: 0.95, 95% confidence interval: 0.92-0.98). Our study demonstrates that not only adults with ASD but also adults with autistic traits are at increased risk for gastrointestinal symptoms, which is associated with psychological and behavioural factors. This suggests that an integrated psychosomatic approach of gastrointestinal symptoms in adults with ASD (traits) is needed.