OBJECTIVE Many symptoms are attributed to teething in infants. There is little evidence to support these beliefs, despite their implications for clinical management. We investigated relationships between tooth eruption, fever, and teething symptoms. METHODS Prospective cohort study. METHODS Twenty-one children 6 to 24 months old attending 3 suburban long-day care centers >/=3 days/week. Measures. 1) Daily temperature recording and examination of alveolar ridges for tooth eruption (dental therapist). 2) Daily questionnaires-symptoms over preceding 24 hours (staff and parents independently). 3) Final questionnaire-beliefs/experiences related to teething (parents). Definitions. Eruption day-the first day a tooth could be seen or felt. Non-toothdays-more than 28 days clear of any eruption day. Toothdays-the 5 days preceding eruption days. RESULTS Data were collected for 236 toothdays and 895 non-toothdays pertaining to 90 teeth. Child temperatures were similar on toothdays and non-toothdays (36.21 vs 36.18, paired t test). Logistic regression adjusted for age did not show an association between toothdays and temperature (odds ratio [OR] = 1.35, 95% confidence interval [CI] = 0.80, 2.27 for high fever; OR = 1.34, 95% CI = 0.48, 3.77 for low fever). Logistic regression models allowing for within-child cluster effects and age were fitted to daily staff and parent reports of mood, wellness/illness, drooling/dribbling, sleep, diarrhea, strong diapers, red cheeks, and rashes/flushing. Only parent-reported (but not staff-reported) loose stools were significantly associated with tooth eruption (OR = 1.86, 95% CI = 1. 26, 2.73). When the toothday definition was varied to 10 days preceding or 5 days surrounding tooth eruption, this single significant association was no longer apparent (OR = 1.42, 95% CI = 0.98, 2.05 and OR = 1.47, 95% CI = 0.97, 2.21, respectively). All parents retrospectively reported that their own children had suffered a range of teething symptoms. CONCLUSIONS This study did not confirm the expected strong associations between tooth eruption and a range of teething symptoms in children 6 to 30 months old, although we cannot rule out the possibility that weak associations may exist (Type II error). These findings contrast with strong parent and professional beliefs to the contrary. Such beliefs may preclude optimal management of common patterns of illness and behavior in young children.teething, infants, symptoms, tooth eruption, illness.