The sturgeon family (Acipenseridae) is gaining considerable attention due to its developing status in fish culture. One of the many unique features of sturgeon is the existence of pericardial nodular lymphoid tissue aggregates. The Atlantic sturgeon (Acipenser oxirinchus), an economically important species of sturgeon, has perhaps received less attention in the literature describing sturgeon morphology and histology. Through histological examination of ten specimens representing two different age classes of Atlantic sturgeon, the structural and functional aspects of the pericardial lymphoid tissue are examined with regard to ontogeny and compared to the existing literature describing these tissues in other species of sturgeon.