Even though eating breakfast is an important factor in health and nutrition, especially during growth stages, skipping breakfast in children and adolescents has increased. An important issue to consider in skipping breakfast is the definition of an adequate or substantial breakfast. To examine what constitutes an adequate breakfast in Korean students, we analyzed breakfast consumption of children and adolescents using alternate definitions of breakfast based on calorie contents and food items eaten in the morning. A total of 1344 participants aged 7-18 years from the Korean National Health and Nutrition Survey (KNHNS) 1998 and 1942 participants from the KNHNS 2001 were included. 84% of students surveyed in 1998 consumed some food, while in 2001; it was down to 79.8%. Students that ate a breakfast which included food from at least two of the main five food groups and had a breakfast intake of food energy greater than 15% of the DRIs were 65.8% in 1998 and 53.1% in 2001. However, when breakfast was defined as the consumption of food from three or more food groups and a intake of food energy greater than 15% of the DRIs, students eating breakfast were 51.2% in 1998 and 39.6% in 2001. As the definition of eating breakfast becomes stricter and includes more foods or more calories, the percentage of students who eat breakfast declines. These results show that using various alternate definitions allow us to assess skipping breakfast in better detail and suggest references for the desirable breakfast.