The purpose was to study self-reported chronic pain and fatigue symptoms among adults with molecularly verified Loeys-Dietz and vascular Ehlers-Danlos syndrome using a cross-sectional questionnaire design. Seventy adults were invited through a National Resource Centre for Rare Disorders. A study specific questionnaire including Brief Pain Inventory, Standardized Nordic Questionnaire, Fatigue Severity Scale, Hospital Anxiety & Depression Scale, questions on physical activity, and disease burden was used. Fifty-two persons participated, n = 34 with Loeys-Dietz and n = 18 with vascular Ehlers-Danlos syndrome, aged 18-68 years, 58% women. Chronic pain (79%) and fatigue (58%) symptoms were common. Half developed pain during childhood/adolescence. Sleep problems and high multi-organ burden were significantly associated with chronic pain (p = 0.004, p = 0.014) and high fatigue (p < 0.001, p < 0.001). Chronic pain was associated with higher scores of fatigue (p = 0.002). Higher scores of fatigue were associated with lower level of physical activity (p = 0.014), higher cardiovascular burden (p = 0.025), and higher symptoms of anxiety (p = 0.001). In this study, symptoms of chronic pain, fatigue, sleep problems, and disease burden seemed to mutually reinforce each other. Initiatives should consider interventions aimed at postponing the onset and reducing symptoms of pain, fatigue, and sleep problems and thus reduce the total disease burden at an early stage in patients with these complex conditions.