(i) This dataset presents macroscopic and microscopic pathological findings and bacteriology of 178 tadpoles diagnosed with Severe Perkinsea Infections. (ii) Specimen were collected and submitted to the NWHC as part of mortality investigations and collection of specimen from apparently healthy populations as part of ongoing amphibian health monitoring. (iii) Necropsies and gross evaluation of carcasses were carried out under a dissecting microscope. (iv) Severe Perkinsea Infection was confirmed in each specimen by histological observation of pathological changes in tissues with presence of Perkinsea-like organisms in at least one organ, including brain, eyes, gastrointestinal tract, gills, heart, liver, lungs, kidney, pancreas, skeletal muscle, skin, spinal cord, spleen, and thyroid gland. (v) For each carcass, the overall extent in percentage, and distribution of the histologic lesions on hematoxylin and eosin slides, the distribution of the Perkinsea-like organisms in different organs (including hypnospore-like and trophozoite-like organisms), and the trophozoite-like/hypnospore-like estimated ratio (T/H) in liver were assessed by a board-certificated veterinary pathologist (MIA). (vi) Fresh liver or spleens of a subset of specimens were processed for bacterial testing.