This study evaluated whether 201Tl scintigraphy can differentiate a central bronchogenic cancer from a distal collapse consolidation. METHODS Nine patients with squamous carcinoma with collapse confirmed by surgery and pathology were included. All patients underwent SPECT 1 hr after an intravenous injection of 3 mCi of 201Tl. Four-hour delayed SPECT was performed in five of the nine patients. The thallium activity in tumor and collapse was visually assessed on the basis of the pathologic findings. The specimens were prepared to have the same orientation and level with the SPECT image. RESULTS The tumor activity appeared higher than that of the collapse in four patients, equal in three patients and lower in two patients. Both collapsed lung with and without superimposed inflammation also showed increased thallium activity. Delayed SPECT aided in tumor detection within a collapsed lung in only two of the five patients. CONCLUSIONS Our study illustrates the need for caution in the interpretation of thallium scintigraphy in patients with central bronchogenic cancer and distal collapse.