The aim of the study was to evaluate the diagnostic accuracy of an informatics-based, noninvasive, prenatal paternity test using array-based single-nucleotide polymorphism measurements of cell-free DNA isolated from maternal plasma.Blood samples were taken from 21 adult pregnant women (with gestational ages between 6 and 21 weeks), and a genetic sample was taken from the corresponding biological fathers. Paternity was confirmed by genetic testing of the infant, products of conception, control of fertilization, and/or preimplantation genetic diagnosis during in vitro fertilization. Parental DNA samples and maternal plasma cell-free DNA were amplified and analyzed using a HumanCytoSNP-12 array. An informatics-based method measured single-nucleotide polymorphism data, confirming or rejecting paternity. Each plasma sample with a sufficient fetal cell-free DNA fraction was independently tested against the confirmed father and 1,820 random, unrelated males.One of the 21 samples had insufficient fetal cell-free DNA. The test correctly confirmed paternity for the remaining 20 samples (100%) when tested against the biological father, with P values of <10(-4). For the 36,400 tests using an unrelated male as the alleged father, 99.95% (36,382) correctly excluded paternity and 0.05% (18) were indeterminate. There were no miscalls.A noninvasive paternity test using informatics-based analysis of single-nucleotide polymorphism array measurements accurately determined paternity early in pregnancy.