BACKGROUND: Previous studies have indicated that the risk of stillbirth is increased in singleton pregnancies achieved after assisted reproduction technology (ART). However, no previous study fully accounted for factors with potential influence on the risk of stillbirth. Further, whether fertility treatment, the possible reproductive pathology of the infertile couples or other characteristics related to being subfertile may explain a possible association with stillbirth remains unclear. This study compares the risk of stillbirth in women pregnant after fertility treatment (IVF/ICSI and non-IVF ART) and subfertile women with that in fertile women. METHODS: We used prospectively collected data from the Aarhus Birth Cohort, Denmark and included information about 20 166 singleton pregnancies (1989-2006). Outcome measure was stillbirth. RESULTS: The risk of stillbirth in women who conceived after IVF/ICSI was 16.2 per thousand ( per thousand) and in women who conceived after non-IVF ART 2.3 per thousand. In fertile and subfertile women, the risk of stillbirth was 3.7 per thousand and 5.4 per thousand, respectively. Compared with fertile women, women who conceived after IVF/ICSI had more than four times the risk of stillbirth [odds ratio (OR): 4.44, 95% confidence interval (CI): 2.38-8.28], and adjustments for maternal age, BMI, education, smoking habits and alcohol and coffee intake during pregnancy had only minor impact on the findings (OR: 4.08; 95% CI: 2.11-7.93). The risk of stillbirth in women who conceived after non-IVF ART and in women who conceived spontaneously with a waiting time to pregnancy of a year or more was not significantly different from the risk in women with a shorter time to pregnancy. CONCLUSIONS: Compared with fertile women, women who conceived by IVF/ICSI had an increased risk of stillbirth that was not explained by confounding. Our results indicate that the increased risk of stillbirth seen after fertility treatment is a result of the fertility treatment or unknown factors pertaining to couples who undergo IVF/ICSI.