Objective To evaluate the frequency of enlarged hilar or mediastinal lymph nodes in heavy smokers (more than 10 pack years) compared with non- smokers. Material and methods In a prospective study the CT findings of 88 consecutive patients (44 heavy smokers, 44 non- smokers) were analysed. Exclusion criteria were history of thoracic malignancy, sarcoidosis, occupational dust exposure or clinical evidence of pneumonia. Prevalence, size and site of enlarged lymph nodes were assessed by multidetector computed tomography (MDCT) and correlated with the cigarette consumption and the CTfindings of bronchitis and emphysema. Results Twenty-three of the 44 heavy smokers (52%) showed enlarged mediastinal lymph nodes. Non- smokers showed enlarged lymph nodes in 9% (4/44). The most common site of enlarged lymph nodes was the regional station 7 according to the ATS mapping (subcarinal). The difference between the frequency of enlarged lymph nodes in heavy smokers and non- smokers was significant (chi- square 19.3, p<0.0001). Airway wall thickening and emphysema were often associated with an increased number of enlarged nodes. Conclusion The present study demonstrates that enlarged mediastinal lymph nodes may occur in a rather high percentage of heavy smokers, especially in those with a MDCT finding of severe bronchitis.