We report on two cases with partial trisomy 1q syndrome. One case was a mid-trimester fetus with multiple malformations that was prenatally diagnosed with a de novo distal partial trisomy 1q. Prenatal ultrasound at 24th gestational week demonstrated the presence of cleft lip and palate, increased biparietal diameter and decreased abdominal circumference. Cytogenetic analysis (GTG banding) and subsequent fluorescence in situ hybridization (FISH) using whole chromosome paint I and multicolor banding (MCB) demonstrated an aberrant karyotype 46,XY,dup(1)(q3 1 q43 similar to 44). The second case was a newborn male infant with multiple congenital malformations. He had a derivative chromosome 18 as a result of a maternal insertion involving chromosomes 1 and 18. Further analyses including MCB showed his karyotype as 46,XY,ins(18;1)(q22;q23q31.1 similar to 32). The present cases and a review of the literature suggest that partial trisomy of the long arm of chromosome I is a distinct clinical entity. Copyright (c) 2007 John Wiley & Sons, Ltd.