We describe a fetus with androgen insensitivity syndrome diagnosed at 16 weeksʼ gestation with two-dimensional (2D) and four-dimensional (4D) sonography and karyotype analysis in a 37year-old pregnant woman. Two-dimensional (2D) sonography revealed a female phenotype. Karyotype analysis revealed an unremarkable 46,XY chromosomal complement. Repeat 4D sonography confirmed a female phenotype with edematous labia majora, consistent with androgen insensitivity syndrome.