A meta-analysis was performed on 68 studies to examine the effect of preoperative instruction on postoperative outcomes. The 68 studies represented 2,413 experimental subjects and 1,605 control group subjects and yielded 423 individual effect sizes. The 423 individual effect sizes had a mean effect size of 0.44 and a variance of 2.43. The mean effect size indicated that, in terms of postoperative outcomes, an average patient who received preoperative instruction was at the 66th percentile of a similar group of patients who did not receive preoperative instruction. The accompanying large variance indicated this finding was not consistent across subject-studies. Substantive characteristics of subject-studies used to categorize effect size were: type of content, method of organization, type of presentation, level of patients' fear/anxiety, and types of outcomes measured. All categories analyzed had positive effect sizes. Within categories of content, psychological and mixed forms of content produced the lowest variances. Categories of organization and presentation did not produce data to demonstrate a clear difference in the levels analyzed. Categories of patient fear/anxiety indicated that the greatest effects were achieved with patients who had high levels of fear/anxiety, followed by moderate levels and low levels. The most consistent results were found with moderate levels of fear/anxiety. When categorized by types of outcomes measured, all effect sizes remained positive. The variances accompanying each effect size remained relatively substantial at all levels of aggregation, with small variances found only at the greatest level of specificity.(ABSTRACT TRUNCATED AT 250 WORDS)