Eighteen strains of L. interrogans isolated from human cases were serotyped by the Agglutinin-absorption test at Instituto Adolfo Lutz in São Paulo, Brazil. Fourteen were identified as serovar copenhageni (Icterohaemorrhagiae serogroup), 2 as canicola (Canicola serogroup), 1 as castellonis (Ballum serogroup) and 1 as Pomona serogroup (serovar not yet defined). The frequency of serovar copenhageni in 100% of the isolates in Icterohaemorrhagiae serogroup is emphasized and more studies to verify the real serovars prevalence as subsidy to the epidemiology of this infection are suggested by the authors