Context: Thyroid dysfunction has been associated with both increased all-cause and cardiovascular mortality, but limited data is available on mild thyroid dysfunction and cause-specific mortality. Objective: To examine the risk of all-cause mortality, major adverse cardiovascular events (MACE), and cause-specific events in subjects with overt and subclinical thyroid dysfunction. Design: Retrospective cohort study. Setting and participants: Subjects who underwent thyroid blood tests, without prior thyroid disease, consulting their general practitioner 2000-2009 in Copenhagen, Denmark. Main Outcome Measure: All-cause mortality, MACE and cause-specific events identified in nationwide registries. Results: 47,327 (8.4%) deaths occurred among 563,700 included subjects (mean age 48.6 [SD ±18.2] years; 39% males). All-cause mortality was increased in overt and subclinical hyperthyroidism (age-adjusted incidence rates [IRs] 16 and 15 per 1000 person-years (py), respectively; incidence rate ratios [IRRs] 1.25 [95% CI: 1.15-1.36] and 1.23 [1.16-1.30]) compared to euthyroid (IR 12 per 1000 py). Risk of MACE was elevated in overt and subclinical hyperthyroidism (IRRs 1.16 [1.05-1.27] and 1.09 [1.02-1.16]) driven by heart failure (IRRs 1.14 [0.99-1.32] and 1.20 [1.10-1.31]). A reduction of all-cause mortality was observed in subclinical hypothyroidism with TSH 5-10 mIU/L (IRR 0.92 [0.86-0.98]). Conclusions: Heart failure is the leading cause of an increased cardiovascular mortality in both overt and subclinical hyperthyroidism. Subclinical hypothyroidism with TSH 5-10 mIU/L might be associated with lower risk of all-cause mortality.