Transcriptome analysis was performed on the thymus of necropsied Japanese Black calves with a poor prognosis, to clarify the pathology of acute thymic involution, which often happens in farmed calves with a poor prognosis. Gene expression profiles obtained by DNA microarray analysis of eight calf thymuses were grouped into three patterns associated with the histopathological classification of acute thymic involution. Three clusters were arranged by the stage of acute thymic involution based on the first principal component score, suggesting that histopathological conditions have the most significant impact on changes in gene expression profile. Overall design: 8 specimens covering all stages of acute thymic involution were selected for transcriptome analysis. No replicates were included. No control samples.