Objective: To compare health service utilization and disability claims among military personnel with multisymptom illness (MSI) (but no chronic diseases), those with chronic disease(s) and those without MSI or chronic diseases. MSI is also known as Gulf War illness. Design: Cohort study. Setting: Australia. Participants: In total, 1288 participants of a Gulf War veterans' study conducted in 2000-2003 (Wave-1) were followed up in 2011-2012 (Wave-2), aged on average 40 years. About 160 had MSI, 217 had chronic disease(s) and 911 had neither chronic disease(s) nor MSI. Methods: At Wave-2, the cohort was linked to the national Medicare and Department of Veterans' Affairs (DVA) databases to obtain health service utilization and disability claims data recorded between 2001 and 2012. Results: The likelihood of visiting a general practitioner (GP) (risk ratio [RR] = 1.04, 95% confidence interval [CI] = 0.92, 1.19) or visiting a specialist medical doctor (RR = 0.83; 95% CI = 0.54, 1.28) or hospitalizations (RR = 0.89; 95% CI = 0.61, 1.29) or) in the 12 months preceding Wave-2 or successfully claiming for DVA disability compensation (RR = 1.13; 95% CI = 0.86, 1.47) was similar for personnel with MSI and those with chronic disease(s). However, GP consultations, hospitalizations, specialist doctor consultations and disability claims were significantly higher among those with MSI than those without MSI/chronic diseases. Conclusions: Health service use and disability claims by personnel with MSI were comparable to those with chronic disease(s), but were in excess of those without MSI/chronic diseases. Hence recognition of the high health service use by personnel with MSI is important to ensure adequate provision of health services.