This research demonstrates that August followed by July are the peak months for Lyme disease reports (1991 to 2000) across the 48 contiguous United States. Eight states have a secondary peak in December. For eleven states disease reports increased, two decreased and 34 had no trend (1991 to 2000). Greatest increases occurred in northeastern states, where the disease is already endemic. Climatic variables in the three months (April, May, June) prior to the summer peak have strong relationships with disease reports/rates. Ninety percent of all cases occur in counties with an average temperature in April, May, June between 10.99 and 17.92C, soil moisture surplus values of 3.43 to 11.00 centimeters, and precipitation values of 23.57 to 33.45 centimeters. The disease system appears to be constrained more by moisture than temperature. The predictive climatic envelope model was used to produce a risk map for Lyme disease.