Cerebral venous thrombosis is a rare condition affecting predominantly adolescents or young adults. The presentation is often non-specific, and delay in diagnosis is common. The otolaryngologist may be consulted about the radiological findings of lateral sinus thrombosis and mastoid changes. The association of congenital thrombophilia with unusual presentations of venous thrombosis, especially in young individuals is now well documented. We present a case of lateral and sagittal sinus thrombosis complicated by cerebral venous infarction in a girl with protein C deficiency and masked mastoiditis. Unusual forms of venous thrombosis, including cerebral venous thrombosis may develop in association with a single risk factor for thrombosis, but additional risk factors should be sought especially when thrombosis presents in very young individuals. This case draws attention to the multi-causal nature of cerebral venous thrombosis in young adults, and highlights the issue of masked mastoiditis. A coordinated approach by otolaryngological and haematological teams is recommended in such cases.