Introduction: To determine if smoking after a cancer diagnosis makes a difference in mortality among newly diagnosed head and neck cancer patients. Methods: Longitudinal data were collected from newly diagnosed head and neck cancer patients with a median follow-up time of 1627 days (N = 590). Mortality was censored at 8 years or September 1, 2011, whichever came first. Based on smoking status, all patients were categorized into four groups: continuing smokers, quitters, former smokers, or never-smokers. A broad range of covariates were included in the analyses. Kaplan-Meier curves, bivariate and multivariate Cox proportional hazards models were constructed. Results: Eight-year overall mortality and cancer-specific mortality were 40.5% (239/590) and 25.4% (150/590), respectively. Smoking status after a cancer diagnosis predicted overall mortality and cancer-specific mortality. Compared to never-smokers, continuing smokers had the highest hazard ratio (HR) of dying from all causes (HR = 2.71, 95% confidence interval [CI] = 1.48-4.98). Those who smoked at diagnosis, but quit and did not relapse-quitters-had an improved hazard ratio of dying (HR = 2.38, 95% CI = 1.29-4.36) and former smokers at diagnosis with no relapse after diagnosis-former smokers-had the lowest hazard ratio of dying from all causes (HR = 1.68, 95% CI = 1.12-2.56). Similarly, quitters had a slightly higher hazard ratio of dying from cancer-specific reasons (HR = 2.38, 95% CI = 1.13-5.01) than never-smokers, which was similar to current smokers (HR = 2.07, 95% CI = 0.96-4.47), followed by former smokers (HR = 1.70, 95% CI = 1.00-2.89). Conclusions: Compared to never-smokers, continuing smokers have the highest HR of overall mortality followed by quitters and former smokers, which indicates that smoking cessation, even after a cancer diagnosis, may improve overall mortality among newly diagnosed head and neck cancer patients. Health care providers should consider incorporating smoking cessation interventions into standard cancer treatment to improve survival among this population. Implications: Using prospective observational longitudinal data from 590 head and neck cancer patients, this study showed that continuing smokers have the highest overall mortality relative to never-smokers, which indicates that smoking cessation, even after a cancer diagnosis, may have beneficial effects on long-term overall mortality. Health care providers should consider incorporating smoking cessation interventions into standard cancer treatment to improve survival among this population.