Autistic children often have comorbid somatic problems. However, in adulthood, this has been much less studied. We investigated the associations between autistic symptoms and irritable bowel syndrome, food allergy, pain, and fatigue in adulthood and examined sex and life-course differences herein. A total of 35,048 adults aged from 18 to 90 from the Lifelines Cohort Study reported autistic symptoms, irritable bowel syndrome, food allergy, pain, and fatigue. Associations between autistic and somatic problems were estimated by logistic and linear regression models. Higher autism scores were associated with more severe somatic problems with an odds ratio of 1.44 (95% confidence interval: (1.34, 1.55)) for irritable bowel syndrome, an odds ratio of 1.13 (95% confidence interval: (1.07, 1.20)) for food allergy, a regression coefficient (b) of 0.20 (95% confidence interval: (0.18, 0.22)) for pain and a regression coefficient (b) of 0.37 (95% confidence interval: (0.35, 0.39)) for fatigue. Associations were stronger in females than males for pain and fatigue. Associations declined with age for fatigue and food allergy and increased with age for irritable bowel syndrome and pain, in a subgroup with autism scores >98th percentile combined with symptom onset in childhood and high functional impairments. These findings are important for autistic adults and may aid in diagnosis, monitoring, and intervention.