Postpartum vaginal atrophy has been briefly noted without adequate clinical description. We present a study of 215 puerperas at a scheduled 4-week postpartum visit, investigating colorpHast vaginal pH, vestibular cotton swab testing, vaginal wall tenderness, and both fixed and wet mount cytologic studies. Thirty-seven patients with vaginal atrophy (17.2%) had a mean pH of 6.55 with a mean maturation index of 49.2% parabasal, 46.5% intermediate, and 4.3% superficial cells. Eighty patients (37.2%) served as control subjects, with a mean maturation index of 0.3% parabasal, 73.6% intermediate, and 26.1% superficial cells, and a mean vaginal pH of 4.68. Ninety-eight patients (45.6%) were excluded for multiple confounding conditions, the most common of which was bacterial vaginosis in 37 (17.2%). This study demonstrates the existence of postpartum vaginal atrophy, notes lactation as an apparent causal factor, and establishes a statistically significant (p less than 0.0001) relationship between vaginal pH and maturation index. Further studies are needed to confirm therapeutic efficacy of estrogens.