Surveys were conducted at four Texas Army National Guard training facilities to assess the natural distribution and prevalence of Thelohania solenopsae Knell, Allen and Hazard infection in polygynous imported fire ants, Solenopsis invicta Buren. T. solenopsae was found at three of the four training facilities; intercolonial prevalence ranged from 9 to 47%, and worker prevalence ranged from 0.15 to 0.57. A plot containing fire ants infected with T. solenopsae at one of the training facilities was monitored for 2 yr to determine whether natural infection rates fluctuate over time, whether infection affects colony size, as indicated by mound volume, and whether there was a relationship between climate and infection prevalence. At this site, intercolonial prevalence ranged from a high of 47% in July 1999 to a low of 11% in October 2000, and mean worker prevalence ranged from 0.20 to 0.57. Mound volume of infected colonies was consistently less than the volume of uninfected colonies. There was no correlation between temperature or precipitation and proportion of infected colonies, but there was a positive correlation between colony density and percentage of infection with T. solenopsae.