BACKGROUND Right retroperitoneal splenosis is rare with few reported cases. We report, here, the case of simultaneous peritoneal and retroperitoneal splenosis mimics metastatic right adrenal mass. METHODS A 28-year-old man who had previously undergone post traumatic splenectomy at childhood and subsequently presented with an large incidental non-functioning right adrenal mass with presence of extra-hepatic peritoneal focal lesion diagnosed as metastasis by magnetic resonance imaging (MRI). Adrenalectomy with metatstectomy was performed, and both masses were identified to be splenosis. CONCLUSIONS Adrenal incidentalomas (AIs) is defined as asymptomatic masses >1 cm. on cross-sectional imaging studies. AIs have significant malignant potential for masses > 6 cm. Splenosis are found most frequently in the left retroperitoneum in cases involving retroperitoneal splenosis. However, right retroperitoneal splenosis have been reported. Traditional imaging techniques cannot differentiate splenosis from malignancy. CONCLUSIONS Large right adrenal incidentalomas present with other abdominal, peritoneal masses could be splenosis in patient following post-traumatic splenectomy.