Between December 2002 and June 2004, 10 marbled salamanders, Ambystoma opacum, were examined for coccidian parasites. Salamanders were collected in Bradley (n = 2), Little River (n = 1), Miller (n = 1), and Sevier (n = 1) Counties, Arkansas; Webster Parish, Louisiana (n = 2); and Bowie (n = 1) and Nacogdoches (n = 2) Counties, Texas. Two of 10 (20%) A. opacum from Louisiana harbored an undescribed species of Eimeria. Oocysts of Eimeria trauthi n. sp. were ellipsoidal, 36.6 × 33.1 (33–40 × 29–37) μm, with a thin, single-layered wall; shape index 1.1. Polar granule(s) and micropyle were absent. Oocyst residuum was composed of hundreds of loosely packed homogenous granules of various sizes enclosing a vacuole. Sporocysts were elongate-ellipsoidal, 20.8 × 8.1 (19–22 × 7–9) μm; shape index 2.6. Sporocyst residuum was spherical and composed of a cluster of granules often membrane-bound. This is the first time a coccidium has been reported from an amphibian species in Louisiana and the second time a coccidium has been described from this salamander host. In addition, the following 26 salamanders from various counties in Arkansas, Oklahoma, and Texas were surveyed during the study period and were negative for coccidia: Ambystomatidae, 4 spotted salamanders (Ambystoma maculatum) and 7 mole salamanders (Ambystoma talpoideum); Cryptobranchidae, 4 Ozark hellbenders (Cryptobranchus alleganiensis bishopi); Plethodontidae, 6 spotted dusky salamanders (Desmognathus conanti) and 3 many-ribbed salamanders (Eurycea multiplicata multiplicata); and Salamandridae, 2 central newts (Notophthalmus viridescens louisianensis).