Thrombocytopenia-absent radius (TAR) syndrome is an autosomal-recessive disorder characterized by a thrombocytopenia and a bilateral radial aplasia with normal thumbs. Only TAR syndrome, out of diseases which may present with radial aplasia, typically has normal thumbs. The prenatal diagnosis is rarely made. We report two observations of TAR syndrome diagnosed in utero in the sibling. The malposition of fetal hands detectable as soon as 11 weeks of gestation requires careful search for longitudinal limb defect of the forearm, especially radial ray defect. The radial aplasia is associated with numerous causes (chromosomal, teratogenic, genetic, multifactorial). The determination of fetal hematologic values revealing a thrombocytopenia allows the prenatal diagnosis of the index case of TAR syndrome.