STUDY OBJECTIVE: To evaluate the immediate cytologic assessment during CT-guided fine-needle aspiration cytology (FNAC) in the diagnosis of operable indeterminate solitary pulmonary nodules (SPNs). DESIGN: Prospective randomized study. PATIENTS AND METHODS: Two hundred twenty patients with SPN undergoing CT-guided FNAC were divided into two groups. In the first one (group A, 110 patients), a cytologist assessed the adequacy of the sample obtained immediately, and when the sample was considered inadequate, fine-needle aspiration (FNA) was repeated. In the second group (B, 110 patients), an immediate cytologic examination was not performed, but only a gross assessment by the surgeon. Histologic study of the SPN was possible in 217 cases, whereas three patients were followed up radiologically. RESULTS: Adequate samples were obtained in 100% of group A and 88% of group B (p<0.001). The diagnostic accuracy was 99% in group A and 81% in group B (p<0.001). Group A required a mean of 1.22 FNAs compared with 1.10 in group B (p=0.015). The rate of pneumothorax in the whole series was 24%, and statistically significant differences between the two groups were not detected. CONCLUSIONS: Immediate cytologic study significantly increased the adequacy and diagnostic accuracy of CT-guided FNAC of indeterminate SPNs without causing a significant increase of complications. (CHEST 1997; 112:423-25)