OBJECTIVE: To identify clinical, laboratory and ultrasonographic evidence of a probable sexually transmitted infection associated with vulvovaginal symptoms in adolescents denying sexual activity. MATERIAL AND METHODS: The medical records of female adolescents, aged 10-18 years were reviewed. These women received first-time medical care for vulvovaginitis, between 1995 and 1999 at Hospital Infantil de México Federico Gómez, (Children's Hospital). Comparisons between groups were performed, as appropriate, by the unpaired Student's t-test, the Z test or the chi-square test; statistically significant differences were set at a two-tailed p < 0.05. Odds ratios with 95% confidence intervals were calculated. RESULTS: Of 258 adolescents with vulvovaginitis, 53 (20.5%) had a sexually transmitted microorganism and 52 of them denied ever having sexual activity. Age, education and socioeconomic level, development of sexual characters, and presence of menstruation did not differ between patients with and without sexually transmitted infections. The presence of sexually transmitted infections was associated with lower abdominal pain, abnormally colored vaginal discharge, a positive urine culture, and an abdominal ultrasonographic evidence, compatible with pelvic inflammatory disease (ultrasonographic odds ratio 144.8; 95% CI 51.0 to 411.3). CONCLUSIONS: There is an association between sexually transmitted infections in young women with vulvovaginitis and lower abdominal pain, abnormally colored vaginal discharge, a positive urine culture, and an abdominal ultrasonographic evidence compatible with pelvic inflammatory disease. The English version of this paper is available too at:http://www.insp.mx/salud/index.html.