Omenn syndrome is characterized by a generalized erythematous skin rash, lymph node enlargement, hepatosplenomegaly, Increased serum IgE levels, eosinophilia, and evidence of severe combined immune deficiency. Patients develop fungal, bacterial, and viral infections. We present the case of a 3-month-old girl with Omenn syndrome who developed right ventricular thrombosis. Echocardiographic study revealed a round structure that filled the apex and corpus of the the right ventricle. We investigated this patient for hypercoagulation and made a diagnosis of ventricular thrombosis, which is an uncommon finding in Omenn syndrome.