This study explored the relationship between electronic media use, sleep and behaviour in preschool-aged children between the ages of three and five years. The primary hypothesis of this study was that excessive electronic media use (>2 hours a day) would positively correlate with sleep patterns (in particular, disturbances) and negative behavioural outcomes (specifically, hostile-aggressive, anxious-fearful and hyperactive-distractible behaviours). Overall, many significant results are reported in support of the main hypothesis. For example, there were strong significant positive correlations between the amount of television (TV) watched and hostile-aggressive, anxious-fearful and hyperactive-distractible behaviours and significant negative correlations between amount of sleep and computer use, video game console use and TV viewing. Implications for teachers and parents are discussed, as well as limitations of the current study and questions in need of further exploration.