A solitary pulmonary nodule (SPN) is defined as a round opacity that is smaller than 3 cm. It may be solid or subsolid in attenuation. Semisolid nodules may have purely ground-glass attenuation or be partly solid (mixed solid and ground-glass attenuation). The widespread use of multidetector computed tomography (CT) has increased the detection of SPNs. Although clinical assessment of patients' risk factors for malignancy--such as age, smoking history, and history of malignancy--is important to determine appropriate treatment, in the recently published Fleischner guidelines for subsolid nodules, smoking history does not factor into their recommendations for management because there is an increasing incidence of lung adenocarcinoma in younger and nonsmoking patients. At imaging evaluation, obtaining prior chest radiographs or CT images is useful to assess nodule growth. Further imaging evaluation, including CT enhancement studies and positron emission tomography (PET), helps determine the malignant potential of solid SPNs. For subsolid nodules, initial follow-up CT is performed at 3 months to determine persistence, because lesions with an infectious or inflammatory cause can resolve in the interval. CT enhancement studies are not applicable for subsolid nodules, and PET is of limited utility because of the low metabolic activity of these lesions. Because of the likelihood that persistent subsolid nodules represent adenocarcinoma with indolent growth, serial imaging reassessment for a minimum of 3 years and/or obtaining tissue samples for histologic analysis are recommended. In the follow-up of subsolid SPNs, imaging features that indicate an increased risk for malignancy include an increase in size, an increase in attenuation, and development of a solid component.