Background: Lung cancer is one of the most common cancers in the world and a major cause of death from cancer. One of the important indicators to compare the prevalence and incidence of the disease is a change in the trend. The aim of this study was to investigate the changes in the incidence of lung cancer in Iran. Materials and Methods: This study was conducted based on existing data obtained from a national registry of cancer cases and the Disease Management Center of Ministry of Health in Iran. All cases registered in the country were included during 2003-2008. Incidence rates were reported based on the direct method and standard population of World Health Organization. The study also examined the morphology of common lung cancers. Trends in incidence underwent joinpoint regression analysis. Results: Based on the results of this study, 14,403 cases of lung cancer have been recorded of which 10,582 cases were in men and 3,821 in women. Highest incidence rates were observed in the 80-84 age group. Considerable variation across provinces was evident. In females squamous cell carcinoma (SCC) demonstrated a reduction from 24% to 16% of lesions over the period of study, while adenocarcinoma rose from 21% to 29%. In males a similar reduction in SCC was apparent (42% to 29%, again with increase in AC (13 % to 18%). Conclusions: The results show that the increase in the incidence of lung cancer the trend is that more men than women and in men and may be caused by changes in smoking pattern. The incidence of lung cancer in the North West and West provinces was higher than in other regions.