We aimed to assess the incidence of multiple primary malignancies in primary lung cancer patients. We retrospectively evaluated the clinical files of 1038 primary lung cancer patients diagnosed in 2004. Forty patients (3.9 %) had multiple primary malignancies. There were 34 men (85 %) and 6 women (15 %). Their mean age was 62.4 +/- 8.6 years. While 35 cases were smokers, 5 cases were nonsmokers. Tumour pathology of the lung was squamous cell carcinoma in 15 cases, adenocarcinoma in 10 cases, small cell carcinoma in 3 cases and non-small cell carcinoma in 12 cases. There were 2 primary tumours in 37 cases and 3 primary tumours in 3 cases. The first detected tumour was located in larynx in 11 cases, in genitourinary system in 9 cases, in intestine in 5 cases, in lung in 3 cases and in other organs in 12 cases. The mean interval between the first and the second tumour was 77 months with a range of 1 months to 32 years. This interval was shorter than 6 months in 4 cases. Treatment modality for the first detected tumour was surgery in 35 cases. The last primary tumour was treated with surgery in 12 cases. In conclusion, the development of multiple primary tumours is not a rare phenomenon. Patients with a malignancy should be followed for development of a second primary malignancy. The treatment of lung cancer in patients with a previous malignancy should be the same as for lung cancers presenting as the first cancer.