A Siamese fighting fish (Betta splendens) showed a whitish, well-demarcated mass on various sites on the body and on the head. Based on histopathological examination, a multifocal iridophoroma was diagnosed in the fish. On H&E-stained slides the iridophores contained fine to coarse golden-brown intracytoplasmic pigment granules, which exhibited white-blue birefringence with polarized light. Additionally, Gram-negative bacteria (Aeromonas hydrophila and Aeromonas veronii) were found in the diseased fish. The present report adds to the sparse literature describing iridophoromas in fish with bacterial infection, spontaneously.