Thallium-201 (Tl-201) is a recognized tumor-imaging agent; however, the usefulness of Tl-201 in bladder cancer has not been studied. The aim of this preliminary study was to evaluate the potential usefulness of Tl-201 in detecting bladder cancer. A total of 14 patients (11 men and 3 women ranging in age from 49 to 80 years) with bladder cancer were arranged for Tl-201 single-photon emission computed tomography (SPECT) of the pelvis. All of the patients had transitional cell carcinoma (TCC). Meanwhile, 7 normal controls (5 men and 2 women; age range: 45-79 years) without any history of pelvic disease also accepted Tl-201 SPECT of the pelvis for comparison. In the result, Tl-201 pelvic SPECT detected bladder cancer in all 14 patients (100.0%). In contrast, all 7 normal controls (100.0%) had negative results of Tl-201 pelvic SPECT. Our study showed that the Tl-201 pelvic SPECT scan could be considered as a useful non-invasive imaging method in detection of bladder cancer.