Previous studies have reported that individual variation in N1 amplitude is related to attentional problems and alcoholism. Using data from 651 twins and siblings from 292 families we examined whether variation in N1 amplitude and latency can be explained by genetic factors. In half of the subjects the age centered around 26 (young adult cohort), in the other half the age centered around 49 (middle-aged adult cohort). Two visual N1 components were identified by a spatial PCA - an early anterior component peaking from 88 to 168 ms after stimulus presentation and a posterior one peaking from 132 to 220 ms. Significant heritability was found for anterior N1 amplitude (22%) and posterior amplitude (50%), and for anterior latency (45%) and posterior latency (43%). We conclude that visual N1 amplitude and latency may serve as endophenotypes to detect genetic variation in susceptibility to psychiatric disorders. © 2007 Elsevier B.V. All rights reserved.