The objectives of this study were to examine serum periplakin expression in patients with urothelial carcinoma of the urinary bladder and in normal controls, and to examine relationships with clinicopathological findings. Detection of serum periplakin was performed in 50 patients and 30 normal controls with anti-periplakin antibodies using the automatic dot blot system, and a micro-dot blot array with a 256 solid-pin system. Levels in patients with urothelial carcinoma of the urinary bladder were significantly lower than those in normal controls (0.31 and 5.68, respectively; p<0.0001). The area under the receiver-operator curve level for urothelial carcinoma of the urinary bladder was 0.845. The sensitivity and specificity, using a cut-off point of 4.045, were 83.7% and 73.3%, respectively. In addition, serum periplakin levels were significantly higher in patients with muscle-invasive cancer than in those with nonmuscle-invasive cancer (P=0.03). In multivariate Cox proportional hazards regression analysis, none of the clinicopathological factors was associated with an increased risk for progression and cancer-specific survival. Examination of the serum periplakin level may play a role as a non- invasive diagnostic modality to aid urine cytology and cystoscopy.