Cystic and cavitary lung lesions constitute a spectrum of pulmonary diseases diagnosed in both children and adults. We reviewed the CT findings of the most common cystic and cavitary lung lesions and we defined useful morphological criteria that will help radiologists to distinguish benign from malignant cavitary lesions. However, in many cases the considerable overlap in morphological features of benign and malignant cavities renders transthoracic needle biopsy necessary to establish the correct diagnosis.