Background: Lung cancer is one of the most commonly diagnosed cancers and the most frequent cause of cancer-related death worldwide. In Iran, it ranks second and third as the cancer-causing death in men and women, respectively. We carried out this study to find out the demographic, clinical, and histological characteristics and risk factors of lung cancer in a referral tertiary center in Iran. Materials and Methods: A retrospective study was conducted on cases of primary lung cancer based on the results of registered cancer reports of cytological and pathological specimens between March 2001 and March 2012. Demographic variables, clinical manifestations, histology and location of tumors were determined based on the data found in the medical records of each patient. Definite or probable etiologic factors were identified. Data analysis was performed with SPSS version 16 and a p-value ${leq}0.05$ was considered as significant. Results: A total of 203 patients, with a mean age of 65.7 years (SD=11.2), with primary lung cancer were identified, 81.3% being men. Of the total, 110 cases (54.2%) were living in urban areas. In 53.2% of cases, the site of tumor was on the right side and in 72.9% of cases the lesion was centrally located. The histological types of lung cancer were squamous cell carcinoma (SCC) in 107 cases (52.7%), adenocarcinoma (AC) in 30 cases (14.8%), and small cell carcinoma (SC) in 27 cases (13.3%). Significant correlations between the gender and residence, smoking, and the histological type and location (central or peripheral) of tumor were found. The percentage of smokers was 75.2% in men and 15.8% in women. Conclusions: Smoking was the most important risk factor and squamous cell carcinoma the most common histological type of lung cancer in our study. Male sex and being a smoker was associated with histological types of SCC while being nonsmoker had relationship with adenocarcinoma.