We describe a case of primary angiosarcoma of the spleen presenting as relapsing haemothorax. An 81-year-old woman was referred to our hospital because of a 2-month history of relapsing haemothorax after the performance of urgent splenectomy due to active bleeding from large spleen cysts. No evidence of neoplasm was seen after pathological examination of the spleen. On admission, left haemothorax and 2 new cystic masses in the thoracic wall were documented, both in close relation to the scars of previous surgery and chest tubes. After excision of 1 mass, histological examination revealed angiosarcoma, and a final diagnosis of primary angiosarcoma of the spleen with postsurgical metastatic dissemination to the thorax and pleura was made. Primary angiosarcoma should be included in the differential diagnosis of haemorrhagic spleen cysts. Clinical diagnosis and management usually requires splenectomy, but it should be carefully planned in order to avoid local metastatic dissemination or haematogenous spread of the tumour. The differential diagnosis of spleen cysts must include malignant conditions.Despite its absolute rarity, angiosarcoma is considered the most common primary non-haematolymphoid splenic malignancy and has a poor prognosis.Splenectomy is usually required for a prompt diagnosis of primary angiosarcoma of the spleen, but it needs to be performed with extreme caution to avoid metastatic dissemination.