Approximately 500 cases of leptospirosis are diagnosed each year in France. Half of these cases occur in the Overseas Departments and Territories, where the incidence rate can be more than 100 times higher than in mainland France. Humans are generally infected through contact with water contaminated by rodent urine. The ministerial decree published in the Official Journal on October 11, 2005, stipulates that the serological diagnosis of leptospirosis must be performed using the macroagglutination screening test, and that the reference method for the serological diagnosis of leptospirosis, the MAT (Microscopic Agglutination Test), must only be used in cases of a positive result by macroagglutination. To evaluate this macroagglutination test as a screening test for the serological diagnosis of leptospirosis, 4,112 serum samples received at the National Reference Center for Leptospira between December 2006 and February 2008 were tested using macroagglutination and MAT. The sensitivity, specificity, positive predictive value, and negative predictive value of this screening test are 62%, 84%, 33%, and 95%, respectively. In conclusion, the macroagglutination test used as a screening test yielded unsatisfactory sensitivity and specificity. Our results show that a significant number of individuals may have leptospirosis despite a negative macroagglutination test. The MAT is a better tool for the diagnosis and identification of circulating leptospira serotypes. (R.A.)