Esotropia with high myopia is due to elongation of the eyeball, which becomes too large to fit within the muscle cone. To demonstrate the elongation, we measured the size of the eyeballs. Five patients with esotropia with high myopia(myopic esotropia group), 8 patients with high myopia without esotropia(high myopia group), and 10 controls(control group) were examined. Using magnetic resonance imaging, we measured the outer axial length and the maximum transverse size of the eyeballs. The outer axial length(mean +/- standard deviation) was greater in the order of the myopic esotropia group(31.6 +/- 1.59 mm), the high myopia group(27.9 +/- 2.22 mm), and the control group(23.7 +/- 1.59 mm) (p < 0.01). The maximum transverse size was also greater in the order of the myopic esotropia group(25.0 +/- 0.99 mm), the high myopia group (24.9 +/- 1.27 mm), and the control group(23.1 +/- 1.38 mm). The outer axial length of the eyeballs in the myopic esotropia group was significantly longer than in the high myopia group and the control group, and the maximum transverse size was significantly longer than in the control group. The elongation of the eyeballs of the myopic esotropia group was demonstrated. A high incidence of esotropia may occur when the outer axial length of high myopia is longer than 30 mm.