Background: Urine cytology has introduced the use of the ThinPrep™ method, originally for gynecologic applications, years ago. It has demonstrated numerous clinically proven advantages, compared to conventional methods. However, the preparation of bladder irrigation fluid has faced several difficulties at the Cytology laboratory at Gävle Hospital, Sweden. The current method, based on the Cytospin® with MegaFunnel™ technique, is soon to be replaced by the ThinPrep™ method at the current lab. The purpose was to compare the ThinPrep™ and the Cytospin® with MegaFunnel™ preparatory techniques. Additionally, investigations for potential improvements of the ThinPrep™ method tailored for the Cytology laboratory at Gävle Hospital was conducted. Material and method: Bladder irrigation fluid was processed using both techniques. The slides were then evaluated by five cytotechnicians and two specialized doctors based on distribution of cells on the smear, the background and assessability for diagnosis. Further investigation of the ThinPrep™ method was conducted for the purpose of optimization. Results: The ThinPrep™ technique showed significant, diagnostical and statistical, improvement in the preparation of bladder irrigation fluid. It successfully detected highly malignant cells, which the conventional method failed to identify. Optimization testing indicated that the method is best suited with appropriate UroCyte™-filters, and the added step of sample-washing removed inflammatory cells and lightened the staining of the smear. Conclusion: The ThinPrep™ technology was proven superior to the conventional Cytospin® technology, providing a cleaner background, clearer staining and – enhanced safety in diagnostic procedure.