BACKGROUND: The Fourth Universal Definition of Myocardial Infarction defines electrocardiographic Q waves as duration ≥30 ms and amplitude ≥1 mm or QS complex in 2 contiguous leads. However, current taskforce criteria may be overly restrictive. Therefore, we investigated the association of isolated, lenient, or strict Q waves with long-term outcome. METHODS: From 2001 to 2015, we included Danish primary care patients with digital electrocardiograms (ECGs) that were evaluated for Q waves. If none occurred, patients had no Q waves. If no other contiguous Q wave occurred, patients had isolated Q waves. If another contiguous Q wave occurred meeting only 1 criterion (≥30 ms and <1 mm or <30 ms and ≥1 mm), patients had lenient Q waves. If another contiguous Q wave occurred, patients had strict Q waves. RESULTS: Of 365,206 patients, 87,957 had isolated, lenient, or strict Q waves (24%; median age, 61 years; male, 48%), and 277,249 had no Q waves (76%; median age, 53 years; male, 42%). Mortality risk was increased with isolated (all-cause adjusted hazard ratio [aHR], 1.33; 95% confidence interval [CI], 1.29-1.37; cardiovascular-cause aHR, 1.78; 95% CI, 1.70-1.87), lenient (all-cause aHR, 1.41; 95% CI, 1.33-1.50; cardiovascular-cause aHR, 1.78; 95% CI, 1.63-1.94), or strict (all-cause aHR, 1.64; 95% CI, 1.57-1.72; cardiovascular-cause aHR, 2.70; 95% CI, 2.52-2.89) Q waves compared with no Q waves. Highest mortality risk was associated with lenient or strict Q waves in anteroseptal leads. CONCLUSIONS: This large contemporary analysis suggests that less-stringent Q-wave criteria carry prognostic value in predicting adverse outcome among primary care patients.