To determine if P300 and other event-related potentials (ERP) could serve as markers for risk of developing alcoholism, two groups of children (8-18 years old) were tested. The high-risk (HR) group consisted of 51 children with an average of 4.1 first- and second-degree relatives who were alcoholic. The low-risk group (LR) consisted of 42 children who had no first- or second-degree relatives who were alcoholic or met criteria for DSM-III Axis I psychopathology. Auditory stimuli varying in conditional probability were presented during a silent counting task, and during a choice reaction task. P300 amplitude was smaller in high-risk than low-risk children. When grouped according to gender and developmental status (8-12 and 13-18 year olds), P300 showed the greatest reduction for the older high-risk males compared to low-risk males. In addition, a previous finding was replicated: the prolonged centro-frontal negativity (232-352 msec), which decreased with age in low-risk children, showed significantly less reduction for high-risk children. Risk status was not related to either amplitudes of the N100 and P200 components of the ERP, or to latencies of any components. Decreases in P300 amplitude and delayed reduction of anterior negativity appear related to developmental processes in high-risk children.