Background/aims: Optic atrophy is one of the leading causes of sight impairment in children. It frequently poses a diagnostic challenge, as it can be caused by many ocular and systemic conditions. We aimed to determine the current causes of optic atrophy at our centre and to describe the use of investigations, including molecular genetic testing. Methods: We reviewed the medical records of children with optic atrophy seen at Moorfields Eye Hospital between 2010 and 2015. We recorded demographic data, reason for referral, history, investigations and diagnosis. Results: We studied 143 cases aged below 16 years. A cause could be identified in all cases. Taking a full history was the most important part of the diagnostic workup, identifying a cause in 96 (67%) children. A developmental disorder of the brain and/or optic nerve, sometimes with retinal involvement, was the commonest cause (n = 33, 23%), followed by inheritable optic neuropathies (n = 27, 19%). Other causes included perinatal insults (n = 18, 13%), post-infectious or post-inflammatory conditions (n = 18, 13%), accidental or abusive trauma (n = 14, 10%) and inheritable retinal dystrophies (n = 13, 9%). Rare conditions included neurodegenerative disorders (n = 7, 5%), skeletal developmental disorders such as rickets (n = 4, 3%), tumours (n = 4, 3%), ischaemic events including large optic nerve head drusen (n = 4, 3%) and toxic events/metabolic conditions (n = 1, 0.7%). Conclusion: In this series, an underlying cause could be identified in all cases. Taking a comprehensive antenatal, perinatal, postnatal and family history will indicate a probable diagnosis in two-thirds of children, and targeted ancillary tests may identify the cause in most remaining cases.