Electroencephalograms during light sleep were performed in controls and in infants with near-miss sudden infant death syndrome, in siblings of such infants, and in infants with recurrent apnea, all from 2 to 8 months of age. EEG background and multiple sleep spindle characteristics were compared for individual children in each of these groups. From 2 to 6 months of age, but not later, all at-risk groups differed from controls by the presence of excessive variability of sleep spindle frequency during sleep recordings. However, the three groups at risk for SIDS did not significantly differ from each other. It is concluded that careful analysis of routine sleep EEGs may in some cases help differentiate young infants at risk for apnea or SIDS from normal children.