A longitudinal cohort study was carried out to determine whether gynaecological infections other than human papillomavirus (HPV) are also related to the subsequent increased risk of cervical neoplasia. The study comprised 19114 women attending the organized mass screening in Finland in 1985-1990 with cytologically detected HPV, Actinomyces, herpes simplex, Trichomonas vaginalis, or yeast. The women were followed-up for subsequent preinvasive lesions and invasive cancers until the end of 1994 by linkage to the nation-wide Cancer Registry. Standardized incidence ratios (SIR) with rates for the whole of Finland as reference and 95% confidence intervals (CI) were estimated. Trichomonas vaginalis and HPV were associated with a high relative risk of cervical cancer, SIR 6.4 (CI 3.7-10, preinvasive lesion and invasive cancer combined) and SIR 5.5 (CI 4.2 7.2, preinvasive lesion and invasive cancer combined), respectively. Herpes simplex was rarely detected, but the highest and statistically most significant point estimate was observed (SIR 12, CI 2.4-34, preinvasive lesion and invasive cancer combined). Neither Actinomyces nor yeast was associated with a significantly increased risk of cervical cancer. None of these results could be accounted for by the confounding effect of the other infections. Our results, based on a prospective design, lead us to propose that Trichomonas vaginalis and herpes simplex virus are also predictors for cervical neoplasia.