Background: Fatigue syndromes affect large numbers of individuals, yet evidence from epidemiological studies on adverse outcomes, such as premature death, is limited. Methods: Cohort study involving 385 general practices in England that contributed to the Clinical Practice Research Datalink (CPRD) with linked inpatient Hospital Episode Statistics (HES) and Office for National Statistics (ONS) cause of death information. A total of 10,477 patients aged 15 years and above, diagnosed with a fatigue syndrome during 2000-2014, were individually matched with up to 20 comparator patients without history of having a fatigue syndrome. Prevalence ratios (PRs) were estimated to compare the fatigue syndrome and comparison cohorts on clinical characteristics. Adjusted hazard ratios (HRs) for subsequent adverse outcomes were estimated from stratified Cox regression models. Outcomes: Among patients diagnosed with fatigue syndromes, we found elevated baseline prevalence of: any psychiatric illness (PR 1.77; 95% CI 1.72-1.82), anxiety disorders (PR 1.92; 1.85-1.99), depression (PR 1.89; 1.83-1.96), psychotropic prescriptions (PR 1.68; 1.64-1.72), and comorbid physical illness (PR 1.28; 1.23-1.32). We found no significant differences in risks for: all-cause mortality (HR 0.99; 0.91-1.09), natural death (HR 0.99; 0.90-1.09), unnatural death (HR 1.00; 0.59-1.72), or suicide (HR 1.68; 0.78-3.63). We did, however, observe a significantly elevated non-fatal self-harm risk: HR 1.83; 1.56-2.15. Interpretation: The absence of elevated premature mortality risk is reassuring. The raised prevalence of mental illness and increased non-fatal self-harm risk indicate a need for enhanced assessment and management of psychopathology associated with fatigue syndromes. Funding: NIHR Greater Manchester Patient Safety Translational Research Centre. Conflict of interest statement: PDW is a member of the Independent Medical Experts Group; an advisory non-departmental public body, which advises the UK Ministry of Defence regarding the Armed Forces Compensation Scheme. In the past, PDW has provided unpaid advice to the UK Department for Work and Pensions regarding mental health issues. PDW does paid consultancy work for a re-insurance company. NK is supported by Greater Manchester Mental Health and Social Care Trust. NK chaired the guideline development group for the 2012 NICE guidelines on the longer term management of self-harm and currently chairs the guideline development group for the NICE depression in adults guideline. NK is also a member of the Suicide Prevention Advisory Group at the Department of Health. Ethical Approval Statement: The study was approved by the independent scientific advisory committee (ISAC) for Clinical Practice Research Datalink research (protocol number: 16_050R).