The impact on cardiovascular events of varying thyroid status and of treatment remains unclarified. The aims of this study were to investigate the association between hyperthyroidism and cardiovascular events in treated and untreated hyperthyroid individuals, as well as exploring the impact of cumulative periods of hyperthyroidism as a proxy for undertreatment on cardiovascular events.The risk of cardiovascular disease was found to be increased in untreated hyperthyroid patients, and the duration of decreased TSH associated with increasing risk of cardiovascular outcomes in both treated and untreated hyperthyroid individuals.