Lung cancer is the leading cause among cancer deaths in the world. Over the recent years, there have been changes in the distribution of the histopathological subtypes of lung cancer. This study was conducted to investigate the changes in the cell-type distribution in lung cancer with regard to age, gender, and smoking history, based on a retrospective analysis of 1195 (94% male, 6% female) proven cases of lung cancer during the period between January 1998 and December 2007. The histopathological subtypes, ages, genders, and detailed smoking histories were obtained from the clinical files. The diagnosis in each patient was confirmed by histopathological samples from the original cancer site in the lung. The patients were divided into two groups: Group I comprised the patients who were diagnosed in the first five years (from January 1998 to December 2002) and Group II comprised the remaining patients (from January 2003 to December 2007). Squamous cell carcinoma (59.1%) was the most common type, followed by small cell carcinoma (21.2%) and adenocarcinoma (13.6%). Over the study period, the incidence of squamous cell carcinoma decreased from 60.1% to 57.8% (a change of -4%, p> 0.05), that of small cell carcinoma decreased from 22.3% to 19.8% (a change of -11%, p< 0.05), and the incidence of adenocarcinoma increased from 11.8% to 15.9% (a change of +30%, p< 0.05). Although squamous cell carcinoma is still the most common type of lung cancer, there has been a significant increase in adenocarcinoma over time that would seem to be due to changes in the characteristics of cigarettes.