Hamartomas are unexpectedly detected in asymptomatic patients, in mass surveys, general health examinations, and chest radiographs for other reasons. They often present a difficult problem both for the radiologist and the referring clinician, as their differentiation from lung carcinoma or a metastasis may be impossible by radiography. Although the typical radiographic appearance of a well circumscribed, solitary, lobulated nodule smaller than 4 cm in diameter with popcorn calcification permits confident recognition, most hamartomas present as noncharacteristic nodules. Some authors, therefore, recommend thoracotomy for a definitive diagnosis. Needle biopsy was helpful in this study for diagnosis in 61 cases. In 42 cases, one procedure requiring two or three punctures was sufficient to obtain the diagnosis; in 17, two procedures (one to three punctures) were required; and in two, three procedures were necessary. Of 61 cases, surgery was performed in 20. The histology of the surgical specimen confirmed the diagnosis except in two cases, in which a benign fibroma and a benign chemodectoma were found. The 5 year follow-up of the 41 cases not operated on showed no evidence of malignancy.