Cervical cytology specimens classified as "unsatisfactory for interpretation" represent a potential source of undetected disease. This prospective study analyzed the potential benefits of a laboratory procedure to reprocess unsatisfactory ThinPrep Pap Tests (Cytyc, Boxborough, MA). All unsatisfactory ThinPrep samples were reprocessed using a glacial acetic acid wash. The study period unsatisfactory rate was compared with that for the previous 12 months. The initial unsatisfactory rate was 1.3% (197/15,154). Of the unsatisfactory ThinPrep samples, 55.8% (110/197) had residual material for reprocessing. After reprocessing, 67.3% (74/110) were reclassified as "satisfactory" or "satisfactory but limited by," and the final unsatisfactory rate was 0.8% (123/15,154), a 62% decrease. Compared with the previous 12-month rate of 0.9% (209/23,730), this was a 12% reduction. Seven (6.4%) of 110 initially classified as unsatisfactory contained an epithelial abnormality (atypical squamous cells of undetermined significance, 3; atypical glandular cells of undetermined significance, 2; low-grade squamous intraepithelial lesion, 1; squamous cell carcinoma, 1) on the reprocessed slide. Reprocessing of unsatisfactory ThinPrep slides yielded additional cellular abnormalities that otherwise would have been undetected. The present study confirms that reprocessing of unsatisfactory ThinPrep slides is a beneficial laboratory procedure.