Objective: (1) To assess
prevalence of urate crystals in synovial fluid. (2) Evaluation of polarizing microscope methods to find urate crystals in synovial fluid. Patients and methods: 30 patients with gout is diagnosed and treated at the rheumatology Department Bach Mai Hospital from 1/2013 to 612014 Method: Pospective, cross-sectional, descrltive. cytological examination and laboratory find urate crystals in synovial fluid were identified under an polarizing microscope. Results: (1) In 30 patients, the rate of urate crystals in joint fluid is 73.3 percent. There is no relationship between rate of urate in synovial fluid with uric acid levels in the blood. Rate of urate crystals in tophi is 77. 7 percent significantly higher than in the fluid. There is no correlation between the rate of urate crystals in the tophi and the forms of tophi. (2) The rate of urate crystals in joint fluid in polarizing microscope methods and non-staining 70 percent and 23.3 percent respectively. Conclusion: The ratio of urate crystals is high in synovial fluid and tophi in polarizing microscope methods. There is correlation between the urate crystals in synovial fluid with the screening method to find urate crystals in early stage of gout.