We evaluated the relationship between immunologic status and vaginal colonization or infection with Candida albicans for 605 women enrolled in a multicenter, prospective cohort study of mother-to-infant transmission of human immunodeficiency virus type 1 (HIV-1). A low CD4+ lymphocyte level (< 14% vs. > or = 14%, which corresponds to an absolute count of approximately 200 x 10(6)/L) was associated with a two- to fivefold increased likelihood of vaginal colonization (odds ratio [OR], 2.28; 95% confidence interval [CI], 1.01-5.19) and vaginal candidiasis (OR, 3.08; 95% CI, 1.21-7.71) during pregnancy and during the postpartum period (OR, 2.98; 95% CI, 1.51-5.88 and OR, 5.45; 95% CI, 1.73-16.6, respectively). These associations persisted in multivariate logistic regression analyses. No associations with CD8+ lymphocyte levels or CD8+ CD38+ or other lymphocyte subset levels were found after adjustment for CD4+ cell level and other covariates. However, postpartum (but not antepartum) antibiotic use and pregnancy were also associated with vaginal colonization and candidiasis (P < or = .001 for each). Vaginal candidiasis was not associated with an increased risk of mother-to-infant transmission of HIV-1; however, a related, more inclusive variable, clinical vaginitis or vaginosis of any etiology at the last antepartum visit, was associated with mother-to-infant transmission (OR, 1.92; 95% CI, 1.07-3.43). These findings emphasize the complex, multifactorial nature of vaginal candidiasis and highlight the need for safe and effective treatment and prevention strategies for women with advanced HIV infection.