To quantify the occurrence of the dipteran parasite Batrachomyia strigapes, the ground frog assemblage associated with a large ephemeral wetland in Western Sydney was sampled between January 1999 and April 2000. Parasite infection was restricted to Uperoleia laevigata (5.1%, n = 1,492). Parasites were found under the parotoid glands, most frequently on the left side. After correction for frog size, infection was shown to significantly reduce frog weight. Despite reduced individual fitness, because the level of infection was low in the population, it is unlikely to have a major effect on the anuran population under current environmental conditions.