In families in which spontaneous miscarriages are very frequent, a systematic search for parental translocations must be made. An examination of the karyotype appears to be justified in patients with three or more miscarriages (probabilily of detecting a translocation equal to or greater than 1 percent). The results of cytogenetic analysis will indicate in many cases the prognosis for subsequent pregnancies and will to a large extent determine the procedure to be followed.