Random-effects meta-analysis comparing folic acid versus placebo for the endpoints of 3 or more adenomas, adenomas greater than or equal to 1 cm in estimated diameter and location in the colorectum. Estimates are unadjusted. Tests for heterogeneity are as follows: For >=3 adenomas, Q=0.99 (P=0.61) and I2=0.0; adenomas >= 1cm, Q=2.30 (P=0.32) and I2=13.0; rectal adenoma Q=2.19 (P=0.33) and I2=8.7; distal adenoma Q=5.32 (P=0.70) and I2=62.4 proximal adenoma Q=3.09 (P=0.21) and I2=35.3. Proximal adenomas include those in the transverse colon, hepatic flexure, ascending colon and cecum; distal adenomas include those in the sigmoid colon, descending colon and splenic flexure. AFPPS, Aspirin/Folate Polyp Prevention Study; NHS/HPFS, Nurses’ Health Study/Health Professional Follow-up Study; ukCAP, United Kingdom Colorectal Adenoma Prevention.