OBJECTIVE To report a new case with partial trisomy 1p due to paternal t(1;9) translocation in a family with recurrent miscarriages. DESIGN Case report. SETTING Faculty of Medicine, Cukurova University. PATIENT(S) A couple with recurrent miscarriages, an abnormal fetus, a newborn infant, paternal grandfather and grandmother. INTERVENTION(S) Chorionic villi sampling (CVS), amniocentesis, lymphocytic karyotype, and genetic counseling. MAIN OUTCOME MEASURE(S) Chromosomal analysis of CVS, amniotic cells, and peripheral blood lymphocytes were performed according to standard cytogenetic methods using G-banding technique. RESULT(S) We determined the reproductive risk in a couple who carried a balance and an unbalanced rearrangement of chromosomes 1 and 9 in two generations of a normal father with derivative 9 karyotype. The prenatal and postnatal karyotypes of the newborn infant were the same as the father [46,XY,der(9)t(1:9)(p34.2;q34.3)]. He was also phenotypically normal. The abnormal fetus that was miscarried also had a derivative 9 [46,XY,der(9)t(1:9)(p34.2;q34.3)fat]. The der(9) contained the partial short arm of chromosome 1. Both chromosome 1 showed normal. Trisomy 1p in the fetus was the result of familial derivative 9. CONCLUSION(S) Partial trisomy is associated with fetal wastage, and may play a role in the etiology of the other miscarriages in certain families. The apparent lack of increased reproductive failure may result from the selective disadvantage of aneusomic gamets at fertilization or very early spontaneous abortions of unbalanced conceptuses. The detection of couples with chromosomal anomalies can undoubtedly help prevent the births of malformed infants. These findings would be used widely in clinical genetics and as an effective tool for genetic counseling and reproductive guidance.