This study was performed to evaluate radiographic healing of teeth with apical periodontitis, treated in one visit or in two visits (a) with or (b) without calcium hydroxide as an intracanal disinfecting medicament. The patients were assigned one of the three treatment groups by the throwing of a die. The Periapical Index (PAI) Scoring Method was used to compare differences in periapical status from the beginning of treatment to a 52-wk follow-up evaluation. Overall, the periapical status of the treated teeth improved significantly after 52 wk (p < 0.0001). A PAI score of 1 or 2 was considered as representing a "good" periapical status while 3, 4, or 5 was a "bad" status. When base line PAI scores were controlled for, the calcium hydroxide group showed the most improvement in PAI score (3, 4, or 5 to 1 or 2), followed by the one-step group (74% vs. 64%). The teeth that were left empty between visits had clearly inferior healing results. Power statistics were conducted to determine the numbers required for significant differences between the groups, and it was shown that large experimental groups on the order of hundreds of patients would be required to show significant differences.