Objective: To investigate the relationship between unexplained elevated second-trimester free β-human chorionic gonadotropin (β-hCG) levels and pregnancy complications as well as adverse pregnancy outcomes. Methods: The study cohort comprised 2,110 non-smoking women with chromosomal and structurally normal fetuses at low-risk for both Down’s syndrome (risk <1:250) and neural tube defects (maternal serum α-fetoprotein <2.0 MoM). A free β-hCG value of ≧2.0 MoM was used to define the populations with elevated levels of free β-hCG. Descriptive statistics, χ2 test, Fisher’s exact test, and logistic regression analysis were used for statistical analysis, and p < 0.05 was considered statistically significant. Results: The mean maternal age of the study group was significantly lower than in controls (27.9 ± 4.3 and 30.6 ± 5.1 years, respectively, p < 0.05), while the proportion of primigravidas was significantly higher compared to that of controls (p < 0.05). After adjustment of the 2 groups according to maternal age and parity, we observed an increased incidence of preeclampsia among women with elevated free β-hCG levels in relation to controls (p < 0.05). However, a logistic regression analysis demonstrated that the free β-hCG level was not a predictor of the occurrence of preeclampsia. No significant relationship was found with the incidence of gestational diabetes, oligohydramnios, polyhydramnios, pregnancy-related hypertension, intrauterine growth retardation, preterm delivery, spontaneous abortion and stillbirths (p > 0.05).