The actual extent of lumen visualized by capsule endoscopy has not been studied systematically. Volunteers were randomized to receive a bowel preparation (prep) consisting of an isotonic solution containing polyethylene glycol and simethicone. The prep (200 ml) was given 30 min before the capsule. The capsule was taken with 100 ml of prep and 100 ml of water; 100 ml of prep was given 45 and 75 min later. The control administration was 100 ml of water and no simethicone. Forty percent of all frames taken in the small bowel were examined and individually scored for circumference, bubbles, debris, and lighting. Nine volunteers were studied twice. Only 50% of the circumference is seen normally. The prep improved the circumference to 62.5% as well as decreasing luminal debris and bubbles and improving the lighting. We conclude that the prep solution improved small bowel visualization, however, improvements are still needed to optimize visualization.