We report a case of cavernous sinus thrombosis in a post-splenectomy male with underlying Haemoglobin E Thalassemia major. A 35-year-old man presented with a first episode of sudden onset of diplopia on lateral gaze for 1 week. He had no other ocular and systemic symptoms. There was no history of trauma or recent infection. However, he admitted that he was not compliant to his oral penicillin V and aspirin, which was prescribed to all post splenectomy patients. Unaided visual acuity in both eyes was 6/6. On examination, there was limited abduction over the left eye, suggestive of left lateral rectus palsy. Full blood count revealed leucocytosis with thrombocytosis. Magnetic resonance imaging, magnetic resonance angiography and magnetic resonance venography of the brain showed bulging of the left cavernous sinus, with a persistent focal filling defect, in keeping with left cavernous sinus thrombosis (CST). He was diagnosed with left isolated sixth nerve palsy secondary to aseptic cavernous sinus thrombosis with pro-thrombotic state post-splenectomy. He was started on subcutaneous fondaparinux and oral warfarin. His diplopia fully resolved after 1 month of treatment with complete resolution of CST on computed tomography venogram.