OBJECTIVE: To measure the use of infertility treatments in the general population and their association with neonatal health. DESIGN: Cross-sectional, population-based study. SETTING: Canton of Vaud, Switzerland; Etude du Developpement des Nouveau-nes (EDEN), a prospective study of chronic childhood conditions. PATIENT(S): Six thousand four hundred seventy-seven live newborns (6,379 pregnancies) delivered of residents of Vaud in the 19 maternity hospitals between 1993 and 1994. MAIN OUTCOME MEASURE(S): Neonatal morbidity, multiplicity, low birth weight, prematurity, intrauterine growth retardation, transfer to intensive care, and length of hospital stay. RESULT(S): Infertility treatments were reported for 2.1% of pregnancies (129 women, 148 newborns) and were associated significantly with adverse outcomes. Population-attributable risks varied from 3%-20%. The outcomes of twins did not differ regardless of whether their mother was treated for infertility. Among singletons, only low birth weight was significantly more frequent when infertility treatments were used. Unadjusted odds ratios for neonatal morbidity were significant only for multiple births (2.56; 95% confidence interval 1.21-5.42). This association was not influenced by maternal characteristics and it disappeared after controlling for sex, gestational age, and birth weight. CONCLUSIONS(S): An independent effect of infertility treatments on neonatal morbidity cannot be ruled out, but most of their impact appeared to be mediated by multiplicity and prematurity. Reducing the number of medically induced multiple pregnancies is the most effective prevention of neonatal morbidity related to infertility treatments. Follow-up studies are needed.