Background In the 1990s outcomes in Danish lung cancer patients were poor compared with the other Nordic countries. The five-year survival was only about 5%, only 10% of patients were operated on and less than 60% received active surgical or oncologic treatment. This paper describes trends in mortality and survival of lung cancer in Denmark from 2000 to 2012. Methods The study population comprised 52 435 patients with a diagnosis of cancer of the trachea and the lung, primarily ascertained from the Danish Lung Cancer Register and grouped into three cohorts by year of diagnosis. The outcome measures covered the first year as well as the first full five-year period after diagnosis and comprised absolute mortality rate (per 100 patient years), absolute survival, and the relative survival. All outcomes were estimated for the overall patient population as well as after stratification by covariates. Results Overall, the mortality rates have declined significantly over time from 117 per 100 patient years to 88 for the one-year mortality and from 75 to 65 for the five-year mortality rates, respectively. With the exception of patients with advanced stage, declining mortality was observed for all strata by gender, comorbidity, stage and surgery status and was accompanied by corresponding improvements in both absolute and relative survival. Conclusions The mortality has been significantly declining and the prognosis correspondingly improving in lung cancer in Denmark since the turn of the millennium. As of today, survival after lung cancer in Denmark is probably in line with the international standard. Based on our results we recommend introducing mortality indicators based on all-cause mortality within the patient population in international benchmarking studies as comparisons based on cancer-specific mortality relative to the total general population may be misleading when interpreted in the context of outcomes and quality of care.