Disseminated neoplasia is reported for the first time in Ameghinomya antiqua (Veneridae) from Chile on the southeastern Pacific coast. A total of 710 clams were collected in winter 2019 and summer 2021 from five sites in three regions: Coquimbo, Biobio, and Los Lagos; all clams were processed by histology. The disease was only detected in clams from the Biobío region. It was characterized by the presence of numerous neoplastic cells with enlarged nuclei and high nuclear to cytoplasmic volume ratios and the almost absence of normal hemocytes. The prevalence did not vary between seasons (7% in winter and 9% in summer).