BackgroundThe metastatic spread of feline lymphoma to the peritoneum (“lymphomatosis”) has been rarely reported in the literature. The sonographic features specific to this rare disease manifestation have not been described and have important treatment and prognostic considerations prompting definitive diagnosis.ObjectivesTo describe the ultrasonic features of feline peritoneal lymphomatosis.AnimalsFour cats with alimentary lymphoma and peritoneal metastasis confirmed using cytology, histology, or both.ResultsThe sonographic features described include either a nonobstructive, focally diffuse, and circumferential intestinal mass, or an eccentric, focally diffuse, gastric mass. The intestinal and gastric lesions exhibited hypo‐to‐anechoic transmural wall thickening with loss of wall layering in association with discrete‐to‐coalescing plaques or sheets of thickened, hypoechoic tissue throughout the mesentery or omenta. All cases exhibited only small volumes of anechoic free peritoneal fluid. Three of the 4 cats also had multiple small hypoechoic nodular foci on the parietal and/or visceral peritoneal surfaces. Two cats had bilateral renomegaly because of lymphoma invasion (2/4) and 1 cat had local lymphadenopathy secondary to lymphoma invasion (1/4).Conclusions and Clinical ImportancePeritoneal lymphomatosis is a rare manifestation of lymphoma metastasis and to date appears to be associated specifically with B‐cell alimentary lymphoma.