The proportion of positive Leptospira microscopic agglutination tests for 23,005 dogs significantly increased from 2002 to 2004 (p < 0.002) regardless of the positive cutoff titer used and was highest (p < 0.05) for serovars Autumnalis and Grippotyphosa. The strongest positive serologic correlation (r = 0.72) was between serovars Autumnalis and Pomona.