Purpose To determine the relationship between retinal ganglion cell (RGC) structure, measured by optical coherence tomography (OCT), and function measured by electrodiagnostic tests in children with suspected optic neuropathy. Methods Children presenting consecutively with suspected optic neuropathy were investigated by visual electrophysiology. ISCEV Standard monocular pattern reversal visual evoked potential (PVEP) P100 and pattern electroretinogram (PERG) P50 and N95, amplitudes and peak times were collected, along with the N95 slope 30 ms after the P50 peak. OCT retinal nerve fibre layer (RNFL) thickness from each peripapillary sector and the average macular RGC volume in a 3.45 mm diameter circle were collated. The sensitivity (SENS) and specificity (SPEC) of abnormal visual electrophysiology measures in predicting OCT structural measures were estimated by receiver operating characteristic (ROC) area under the ROC curve (AUC). Results Monocular PVEPs and PERGs from 30-degree stimulus fields and OCT RNFL and RGC volume were available from 42 children (84 eyes) aged 5.5–16.3 years (median 12.4 years). PVEP AUC was highest for predicting both RGC macular volume and temporal RNFL thinning (SENS 88%, SPEC 88%), followed by the PERG N95 slope (SENS 79%, SPEC 78%). PERG N95:P50 had the lowest SENS of 62% and SPEC of 61%, which were similar for all RNFL sectors. Conclusion Abnormal PERG N95 slopes and PVEPs predicted severe loss of macular RGC volume and temporal sector RNFL with high diagnostic accuracy. These measures are important additions to the less specific PERG N95:P50, which was broadly sensitive to all RNFL sectors. The N95 slope and PVEPs are valuable objective functional markers of RGC health in children.