Lung cancer (LC) is a major public health problem and it is the most common form of cancer in men. It remains the most common cause of cancer death in men and women. In the initial decades of the smoking-caused epidemic, squamous cell carcinoma was the most frequent type. Recently there was a shift toward predominance of adenocarcinoma. The aim of our retrospective study was to compare the demographic factors and factors connected with the disease in patients whose LC was diagnosed in two distinct periods in H.S. João (1979-1982 and 1999-2002). A total of 750 LC were diagnosed. Between 1979-1982 a total of 236 patients were diagnosed LC (84.3% male; mean age 60.0 +/- 10.0). The most common histological type was squamous cell (46.2%). A total of 514 LC were diagnosed during the period 1999-2002 (83.9% male; mean age 64.7 +/- 10.8) and adenocarcinoma was the most frequent (47.1%). There were significant differences, between the two periods analysed concerning smoking (increase in the number of smokers; 73.7% vs 82.4%), age (increase in the mean age of patients) and histology (higher percentage of ade notnocarcinoma and reduction of squamous cell and small-cell lung cancer). The percentage of patients treated symptomatically decreased significantly in 20 years (26% vs 19%). As a conclusion we can say that there was an evolution of histological types in the last two decades and a reduction in the number of patients submitted to symptomatic treatment alone.